WORKS  OF 
ARTHUR  H.  BLANCHARD,  C.E.,  A.M. 

Published  by 

JOHN  WILEY  &  SONS,  Inc. 


Elements  of  Highway  Engineering.     A  Short  Text- 
Book  Designed  for  Students  in  Civil  Engineering  Courses. 
8vo,  xiii  +  497  pages,  202  figures.    Cloth,  $3.00  net. 

Section  15,  Highways  and  Streets,  in  American  Civil 
Engineers'  Pocket  Book. 


By  ARTHUR  H.  BLANCHARD,  C.E.,  AM. 

AND 

HENRY  B.  BROWNE,  C.E. 


ay  Engineering.  A  Comprehen- 
sive Text-Book  for  Students  and  a  Reference  Work  for 
Engineers. 

8vo,  xiii  +  762  pages,  234  figures.    Cloth,  $4.50  net. 

Highway  Engineering,  as  Presented  at  the   Second 
International  Road  Congress,  Brussels,  1910. 

8vo,  v  +  299  pages.    Cloth,  $2.00  net. 


ELEMENTS      f 

OF 

HIGHWAY  ENGINEERING 


BY 
ARTHUR  H.  BLANCHARD,  C.E.,  A.M. 

Professor  in  charge  of  the  Graduate  Course  in  Highway  Engineering  in  Columbia  University 
in  the  City  of  New  York;  Consulting  Highway  Engineer;  Member,  American  Society 
of  Civil  Engineers,  Societ6  des  Ingenieurs  Civils  de  France,  Canadian 
Society  of  Civil  Engineers,  Association  Internationale  Perma- 
nente  des  Congres  de  la  Route,  Association  Inter- 
nationale pour  1'Essai  des  Materiaux. 


FIRST  EDITION 
FIRST  THOUSAND 


NEW   YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:  CHAPMAN  &  HALL,  LIMITED 
1915 


Copyright,  1915,  by 
ARTHUR  H.  BLANCHARD 


PUBLISHERS  PRINTING  COMPANY 
207-217  West  Twenty-fifth  Street,  New  York 


PREFACE 

THIS  book  has  been  written  at  the  suggestion  of  several 
professors  of  civil  engineering  who  desire  to  use  a  didactic 
text,  covering  the  principles  of  highway  engineering,  of  such 
length  as  to  be  suitable  for  one-semester  courses  included  in 
civil  engineering  curricula.  The  text  of  this  work  is  made  up  of 
original  manuscript,  and  also  of  material  from  the  "  Text-book 
on  Highway  Engineering,"  by  Blanchard  and  Drowne,  which 
has  been  revised  and  remodelled  to  meet  the  requirements  of  a 
book  suitable  for  use  by  engineering  students  who  take  courses 
in  highway  engineering  aggregating  from  one  to  three  hours  a 
week  for  one-half  of  the  collegiate  year.  It  should  be  noted 
that  the  "  Text-book  on  Highway  Engineering"  was  designed 
to  be  a  comprehensive  text  for  highway  engineering  students 
and  a  reference  book  for  engineers. 

Each  chapter  of  the  "Elements  of  Highway  Engineering" 
has  been  written  with  a  view  to  emphasizing  the  fundamental 
principles  which  have  been  evolved  from  past  experience  as  well 
as  from  the  modern  practice  of  highway  engineering  which, 
as  a  science  and  an  art,  is  rapidly  developing  in  the  fields  of 
economics,  administration,  legislation,  materials,  and  methods. 
Specifications,  per  se,  examples  of  construction,  and  detailed  cost 
data  have  been  omitted,  as  such  material  is  not  considered 
essential  to  a  broad  general  knowledge  of  the  science  of  high- 
way engineering.  The  text  of  the  chapters,  occupying  450  pages, 
has  been  profusely  illustrated  with  202  figures,  equivalent  in 
space  to  85  pages. 

As  the  nomenclature  of  materials  and  methods  of  construc- 
tion and  maintenance  may  be  confusing  to  the  student,  a  glossary, 
constituting  Appendix  I,  has  been  included.  Appendices  II  and 


VI  PREFACE 

III,  containing,  in  detail,  methods  for  determining  physical  and 
chemical  properties  of  bituminous  and  non-bituminous  highway 
materials,  will  be  found  of  value  to  professors  who  wish  to 
elaborate  upon  the  subject  of  essential  properties  of  materials 
and  their  determination. 

For  a  course  constituting  one  hour  a  week  for  a  half  year, 
it  is  suggested  that  the  subject  matter  might  be  reduced  in 
amount  by  the  omission  of  the  text  covering  examples  of  state 
legislation,  pages  31  to  36;  surveying  and  mapping,  pages  64  to 
75;  mining  and  manufacture  of  bituminous  materials,  pages  196 
to  210;  interpretation  of  tests  of  bituminous  materials,  pages 
214  to  222;  descriptions  of  machines,  pages  98  to  in,  241  to 
247,  and  288  to  293;  sidewalks,  curbs,  and  gutters,  pages  406 
to  420;  and  highway  structures,  pages  421  to  450.  The  total 
number  of  pages  thus  eliminated  amounts  to  about  no. 

The  author  gratefully  acknowledges  his  indebtedness  to  the 
engineers  and  chemists  whose  writings  he  has  quoted,  to  technical 
periodicals  for  certain  tables  and  cuts,  and  to  numerous  manu- 
facturers for  furnishing  photographs  to  illustrate  the  text. 

The  author  requests  that  users  of  this  work  as  a  text-book 
submit  suggestions  pertaining  to  elaboration  or  reduction  of  the 
several  sections  of  the  book  to  meet  individual  requirements.  It 
is  also  requested  that  readers  call  the  attention  of  the  author 
to  errors  which  may  occur  in  the  text.  Cooperation  along  the 
above  lines  will  be  appreciated. 

A.  H.  B. 

COLUMBIA  UNIVERSITY, 
NEW  YORK  CITY, 
September  i,  1915. 


TABLE  OF  CONTENTS 

CHAPTER  I 

PAGE 

HISTORICAL  REVIEW       . i 

Ancient  Highways  of  the  Eastern  Hemisphere — Early  Grecian 
Highways — Early  Roman  Highways — Early  French  Highways — 
Early  British  Highways — Early  American  Highways. 

CHAPTER  II 

ECONOMICS,  ADMINISTRATION,  LEGISLATION,  AND  ORGANIZATION      .      .       16 

Economics — Benefits  of  Improved  Highways — Financing  High- 
ways— Labor  Tax — Convict  Labor — Direct  Taxation — Direct  Ap- 
propriation— Bond  Issues — Private  Subscription — Administration 
and  Legislation — France — Germany — Great  Britain — United  States 
— Municipalities — Organization — State  and  County  Departments — 
Urban  District  Departments. 

CHAPTER  III 

PRELIMINARY  INVESTIGATIONS .......       44 

Location — Foundations — Drainage — Width — Local  Materials — 
Climatic  Conditions — Maintenance — Local  Environments — ^Es- 
thetics — Traffic — Traffic  Classification — Effect  of  Different  Classes 
of  Traffic— Loads  and  Tire  Widths— Methods  of  Taking  Traffic 
Census. 

CHAPTER  IV 

SURVEYING,  MAPPING,  AND  DESIGN 64 

Surveys  for  Roads — The  Transit  Line — Levels — Final  Surveys — 
Staking  Grades — Mapping  Road  Surveys — Plan — Profile — Cross- 
Sections — Surveys  for  City  Streets — Traverse — Levels — Mapping 
Street  Surveys — Design  of  State  Highway  Systems,  City  Highway 
Systems,  and  Park  Highway  Systems — Scope  of  Highway  Design 
— Location — Widths  of  Roads,  Streets,  and  Park  Highways — 
Grades — Street  Intersections — Curves — Cross-Sections  of  Roads 
and  Streets — Crown  Formulas — Drainage  and  Foundations — 
Selection  of  Type  of  Wearing  Course. 


Vlll  ELEMENTS    OF   HIGHWAY   ENGINEERING 

CHAPTER  V 

PAGE 

GRADING,  DRAINAGE,  AND  FOUNDATIONS    .     .     .     .     .    ...•"%•.'>    .      94 

Grading — Excavation — Embankment — Classification  of  Mate- 
rials— Shrinkage  of  Materials — Machines — Road  Drags,  Scrapers, 
Elevating  Graders,  Rollers,  and  Scarifiers — Drainage — Subdrainage 
— Pipe  Drains — Surface  Drainage — Side  Ditches  and  Gutters — 
Foundations — Classification — Natural  Foundations — Soil  Classifi- 
cation— Loads  on  the  Foundation — Artificial  Foundations — Stone 
Foundations — Telford  Foundations — V-Drain  Foundations — Broken 
Stone  Foundations — Cement-Concrete  Foundations — Foundations 
Over  Marshes — Old  Pavements  as  Foundations — Bituminous  Con- 
crete Foundations. 

CHAPTER  VI 

EARTH  AND  SAND-CLAY  ROADS   .      .      .     .     .     .     .     .     .      .     r     .     128 

Occurrence — Soils — Sand,  Clay,  and  Sand-Clay  Construction — 
Drainage — Wearing  Course  of  Earth  Roads — Wearing  Course  of 
Top  Soil  Roads — Roads  with  Sandy  Subsoil — Roads  with  Clayey 
Subsoil — Burnt  Clay  Roads — Straw  Roads — Petrolithic  Roads — 
Maintenance — Drags  vs.  Scrapers — Road  Drag  Regulations. 

CHAPTER  VII 

GRAVEL  ROADS .     ....     .     141 

Development — The  Gravel — Formation  and  Occurrence — Requi- 
sites of  Gravel — The  Binder — Testing  Gravel — Mechanical  Analysis 
— Construction — Preparation  of  Subgrade — Construction  of  the 
Wearing  Course — Sizes  of  Gravel — Thicknesses  of  Courses — Spread- 
ing and  Compacting  the  Gravel — Cost  Data — Maintenance. 

CHAPTER  VIII 

BROKEN  STONE  ROADS      .      .     ,     . 154 

Rock  Classification — Essential  Properties  of  Rock — Testing  the 
Rock — Abrasion,  Cementing  Value,  Toughness,  Hardness,  Absorp- 
tion, and  Specific  Gravity — Quarrying  and  Crushing — Drilling — 
Blasting — Crushing  Plants — Voids  and  Weights  of  Crushed  Stone 
— Construction — Tresaguet's  and  McAdam's  Methods — Sizes  of 
Broken  Stone — Foundation  and  Subgrade — Construction  of  the 
Courses — Miscellaneous  Roads — Slag  Roads — Shell  Roads — Cost 
Data — Maintenance — Causes  of  Wear — Ordinary  Repairs — Resur- 
facing— Characteristics. 

CHAPTER  IX 

BITUMINOUS  MATERIALS    ....". 192 

Definitions  of  Bituminous  Materials  and  Methods  of  Use — 
Sources,  Mining,  and  Manufacture — Rock  Asphalts — Asphalts — 
Trinidad  and  Bermudez  Asphalts — Alcatraz  Asphalt — Gilsonite 


TABLE    OF    CONTENTS  ix 

PAGE 

BITUMINOUS  MATERIALS — Continued        *.      .     .     .      192 

Asphalt — Petroleums — Tars — Gas-House  Coal  Tar — Coke  Oven 
Tar — Water  Gas  Tar — Tests  and  Specifications  for  Physical  and 
Chemical  Properties — Lists  of  Tests — Brief  Descriptions  of  Tests — 
Interpretation  of  Results  of  Tests — Utilization  of  Tests  in  Specifi- 
cations. 

CHAPTER  X 

DUST  PREVENTION  AND  BITUMINOUS  SURFACES 227 

Dust  Prevention — Classification  of  Surface  Treatment  Methods 
— Development — Formation  of  Dust — Pathogenic  and  Other  Effects 
of  Dust — Use  of  Palliatives — Classification  of  Palliatives — Watering 
— Calcium  Chloride — Emulsions — Light  Oils  and  Light  Tars — 
Bituminous  Surfaces — Bituminous  Materials — Construction  Meth- 
ods— Maintenance — Mechanical  Appliances — Gravity  and  Pres- 
sure Distributors — Characteristics — Advantages — Disadvantages 
— Causes  of  Failure. 

CHAPTER  XI 

BITUMINOUS  MACADAM  PAVEMENTS       .      .     .  .     .     ...      .     253 

Development — Bituminous  Materials — Construction — Methods 
of  Construction  Using  Broken  Stone — Methods  of  Construction 
Using  Gravel — Cost  Data — Maintenance — Characteristics. 

CHAPTER  XII 

BITUMINOUS  CONCRETE  PAVEMENTS       .      .      .      ...     .     .     .;   .     267 

Development — Mineral  Aggregates — One  Product  of  a  Crushing 
Plant — Combinations  of  Broken  Stone  and  Fine  Material — Mechan- 
ically Graded  Aggregates — Topeka,  Asphalt  Block,  and  Bitulithic 
Pavements — Patents — Bituminous  Materials — Bitumen  Content — 
Wearing  Course  Mixtures — Construction — Subgrade  and  Founda- 
tion— Wearing  Course — Manufacture  and  Laying  of  Asphalt  Blocks 
— Mechanical  Appliances — Cement-Concrete  Mixers — Mixers  with 
Heating  Attachments — Dryers,  Storage  Bins,  and  Mixers — Cost 
Data — Maintenance — Characteristics. 

CHAPTER  XIII 

SHEET  ASPHALT  AND  ROCK  ASPHALT  PAVEMENTS 298 

Development — Materials  for  Sheet  Asphalt  Pavements — Asphalt 
Cement — Binder  Stone — Sand  and  Filler  for  Wearing  Course — 
Construction  of  Sheet  Asphalt  Pavements — Subgrade  and  Founda- 
tion— Binder  Course — Wearing  Course — Asphalt  Plants — Rock 
Asphalt  Pavements — European  Practice — American  Practice — 
Cost  Data — Maintenance  of  Sheet  Asphalt  Pavements — Repairs 
and  Conditions  of  Guarantee — Characteristics. 


X  ELEMENTS   OF   HIGHWAY   ENGINEERING 

CHAPTER  XIV 

PAGE 

CEMENT-CONCRETE  PAVEMENTS     .      .      .     .',*.*.•.'       315 

Development — Cement-Concrete — Construction — Subgrade  and 
Foundation — Methods  of  Construction — Mixing  Methods — One- 
Course  Pavement — Two-Course  Pavement — Reinforced  Pavements 
— Oil  Cement-Concrete — Expansion  Joints — Grouting  Method — 
Bituminous  Surfaces  on  Concrete — Cost  Data — Maintenance — 
Characteristics. 

CHAPTER  XV 

WOOD  BLOCK  PAVEMENTS       .     .   V    .    •'. '   •     ...     .     .     .      .     328 

Development — The  Wood — Wood  Preservation — Manufacture 
of  Blocks — Construction — Subgrade  and  Foundations — Cushion 
Layers — Construction  of  Wearing  Course — Fillers — Cost  Data — 
Maintenance — Characteristics. 

CHAPTER  XVI 

BRICK  PAVEMENTS .    ,.     -.,   4     .      •      •     344 

Development — The  Brick — Brick  Clays  and  Shales — Size  of 
Brick — Testing  the  Brick — Construction — Subgrade  and  Founda- 
tion— Cushion  Courses — Methods  of  Laying  the  Brick — Joint 
Fillers  and  Expansion  Joints — Cost  Data — Maintenance — Charac- 
teristics. 

CHAPTER  XVII 

STONE  BLOCK  PAVEMENTS        .      .     „ 363 

Development — Stone  Blocks — The  Stone — Manufacture  of 
Blocks — Size  of  Blocks — Tests  for  Stone  Blocks — Construction — 
Subgrade  and  Foundation — Cushion  Layers — Construction  of 
Wearing  Course — Joint  Fillers — Durax  and  Kleinpflaster  Pave- 
ments— Stone  Trackways — Cobble  Stone  Pavements — Clinker  and 
Slag  Block  Pavements — Cost  Data — Maintenance — Characteristics. 

CHAPTER  XVIII 

STREET  CLEANING  AND  SNOW  REMOVAL     ..-."...     .      .      .     376 

Street  Cleaning — Hand  Cleaning — Machine  Sweeping — Hose 
Flushing — Machine  Scraping  and  Flushing — Methods  Applicable 
to  Various  Types  of  Roads  and  Pavements  in  Urban  Districts — 
New  York — Philadelphia — Boston — Washington,  D.  C. — Great 
Britain — France — Germany — Snow  Removal — Removal  by  Ma- 
chines— Removal  by  Use  of  Salt — Removal  by  Flushing. 


TABLE    OF    CONTENTS  xi 

CHAPTER  XIX 


i 

PAGE 


COMPARISON  OF  ROADS  AND  PAVEMENTS    .      .      .     ;     .      .      .      .      .     389 

Development — Essentials  of  An  Ideal  Road  or  Pavement — 
Durability — Sanitary  Qualities — Noiselessness — Slipperiness — Re- 
sistance to  Traffic — Annual  Cost — Methods  of  Comparison — 
Records  and  Cost  Data  Forms. 


CHAPTER  XX 

SIDEWALKS,  CURBS,  AND  GUTTERS   ......     .      .     .      .     .      .     406 

Sidewalks — Essential  Qualities — Width  and  Slope  of  Sidewalks — 
Materials — Construction  Methods — Cost  Data — Asphaltic  Mastic 
— Brick  and  Tile — Cinders — Cement  -  Concrete — Gravel — Small 
Stone  Setts — Stone  Flagging — Curbs — Stone  and  Cement-Concrete 
Curbs — Gutters — Methods  of  Construction — Cost  Data. 


CHAPTER  XXI 

HIGHWAY  STRUCTURES .     421 

Bridges  and  Culverts — Determination  of  Waterway — Culverts — 
Design,  Location,  and  Construction — Vitrified  Pipes — Cast- Iron 
Pipes — Corrugated  Metal  Pipes — Stone  Box — Reinforced  Concrete 
Box — Drop  Inlets — Catch-Basins — Bridges — Design,  Location,  and 
Construction — Steel,  I -Beam,  Pony  Truss,  Plate  Girder,  Concrete, 
and  Reinforced  Concrete  Bridges — Guard  Rails — Wood,  Pipe,  and 
Concrete  Rails — Highway  Signs — Road  Signs — Direction,  Distance, 
and  Danger  Signs — Highway  Department  Signs — Street  Signs — 
Car  Tracks — Location — Track  Construction — Rails — Surfacing  Ad- 
jacent to  Rails — Pipe  Systems — Design  and  Location — Repaving 
Trenches. 

APPENDIX  I 
GLOSSARY  OF  TERMS  APPLICABLE  TO  HIGHWAY  ENGINEERING      .      .      .451 


APPENDIX  II 

TESTS  FOR  BITUMINOUS  MATERIALS ,      .     466 

Specific  Gravity — Flash- Point — Solubility  in  Carbon  Disulphide 
— Solubility  in  Carbon  Tetrachloride — Consistency — Viscosity  Test 
— Float  Test — Penetration  Test — Melting  Point — Loss  on  Evapora- 
tion— Distillation — Ductility — Solubility  in  Petroleum  Naphtha 
and  Character  of  Residue  on  Glass — Fixed  Carbon — Paraffin. 


xil  ELEMENTS    OF   HIGHWAY   ENGINEERING 

APPENDIX  III 

TESTS  OF  NON-BITUMINOUS  MATERIALS  < 

Apparent  Specific  Gravity  of  Rock — Apparent  Specific  Gravity 
of  Sand,  Stone  Screenings,  or  Other  Fine  Highway  Material — 
Absorption  of  Water  per  Cubic  Foot  of  Rock — Abrasion  Test  for 
Broken  Stone  or  Broken  Slag — Abrasion  Test  for  Gravel — Tough- 
ness Test  for  Rock  or  Slag — Hardness  Test  for  Rock  or  Slag — 
Cementation  Test  for  Rock,  Slag,  or  Gravel  Powder — Mechanical 
Analysis  of  Broken  Stone,  Broken  Slag,  or  Gravel — Mechanical 
Analysis  of  Sand  or  Other  Fine  Highway  Material — Mechanical 
Analysis  of  Mixtures  of  Sand  or  Other  Fine  Highway  Material  and 
Broken  Stone,  Broken  Slag,  or  Gravel — Voids  in  Mineral  Aggregates 
— Rattler  Test  for  Paving  Brick. 


ELEMENTS  OF 
HIGHWAY  ENGINEERING 


CHAPTER  I 
HISTORICAL  REVIEW* 

IT  is  the  purpose  of  this  chapter  to  give  a  broad  general 
review  of  the  development  of  the  art  and  science  of  highway 
building  to  about  A.D.  1840.  Many  of  the  various  forms  of 
modern  pavements  were  not  introduced  until  after  this  date. 
Since  the  later  developments  are  intimately  connected  with  the 
details  of  construction  of  roads  and  pavements,  the  historical 
review  relative  to  each  type  will  be  of  greater  value  if  included 
in  the  chapter  to  which  it  specifically  refers. 

ANCIENT  HIGHWAYS  OF  THE  EASTERN  HEMISPHERE.  The 
economic  value  of  highways  in  its  broadest  sense  was  not  ap- 
preciated as  much  by  the  ancient  races  as  it  is  to-day.  The 
primary  object  of  the  roads  built  by  them  was  to  facilitate  the 
movements  of  troops  rather  than  for  the  development  of  com- 
mercial, industrial,  agricultural,  and  social  interests.  History 
previous  to  1900  B.C.  is  rather  vague  concerning  the  subject  of 
highways.  Herodotus  tells  of  a  road  which  was  constructed 
about  4000  B.C.  and  over  which  materials  of  construction  used 
in  building  the  pyramids  were  supposed  to  have  been  hauled. 
Although  Biblical  history  mentions  in  several  instances  that 
there  were  public  highways,  the  first  roads  of  which  there  is 
any  authentic  record  are  those  in  the  Assyrian  Empire  built 
about  1900  B.C.  These  roads  radiated  from  Babylon,  and  the 
remains  of  one  can  still  be  seen  to-day  between  Bagdad  and 
Ispahan.  This  road,  as  well  as  the  oldest  bridge  on  record  of 

*  Prepared  by  Mr.  Henry  B.  Drowne,  Instructor  in  Highway  Engineering 
in  the  Graduate  Course  in  Highway  Engineering,  Columbia  University,  and 
Engineer,  Lane  Construction  Corporation. 

1 


OF^HIGHWAY  ENGINEERING 

any  importance,  which  is  that  over  the  River  Euphrates  near 
Babylon,  was  built  during  the  reign  of  Queen  Semiramis. 

EARLY  GRECIAN  HIGHWAYS.  History  is  not  very  definite  as 
to  the  methods  of  construction  of  the  roads  of  ancient  Greece. 
Many  of  these  roads  were  built  as  approaches  to  religious  temples. 
One  of  the  principal  roads  led  from  Athens  to  Eleusis,  and 
served  as  a  means  of  communication  with  Peloponnesus,  Thebes, 
and  Phocis,  and  the  greater  part  of  the  North.  The  Greeks, 
according  to  some  authorities,  were  not  as  attentive  to  drainage, 
in  connection  with  the  construction  of  their  roads,  as  were  the 
Romans.  They  paved  their  roads  with  large  square  blocks  of 
stone.  The  royal  roads  of  Greece  were  under  the  authority  of 
the  Athenian  Senate,  which  levied  taxes  for  the  maintenance 
of  the  roads.  In  some  of  the  largest  cities,  such  as  Thebes, 
the  care  of  the  streets  was  intrusted  to  a  person  of  high  rank. 

EARLY  ROMAN  HIGHWAYS.  According  to  Isadore  de  Seville, 
who  lived  in  A.D.  700,  the  Carthaginians  were  the  first 
to  build  paved  roads.  Their  methods  were  later  copied  by  the 
Romans.  Carthage  flourished  from  about  600  B.C.  to  146  B.C., 
at  which  time  this  empire  was  destroyed  by  the  Romans.  The 
Romans  built  roads  on  a  more  extensive  scale  than  any  of  the 
other  nations.  Road  building  was  a  state  policy  in  the  Roman 
Empire.  Gautier  says  that  the  Romans  divided  their  roads 
into  the  following  classes:  royal  roads,  vicinal  roads,  and  private 
roads.  The  royal  roads  included  the  main  military  roads  which 
traversed  all  of  Europe  and  the  northern  part  of  Africa.  The 
vicinal  roads  connected  the  royal  roads  with  the  towns  or  cities. 
The  private  roads  connected  the  royal  roads  or  vicinal  roads 
with  some  particular  locality  other  than  a  town  or  city.  By 
means  of  this  system  of  roads  the  whole  of  the  Roman  Empire 
could  be  readily  traversed.  Soldiers  were  able  to  travel  as 
much  as  twenty  miles  a  day  over  these  roads. 

During  the  reign  of  the  kings,  the  Roman  roads  were  doubt- 
less constructed  of  the  natural  soil.  In  the  year  311  B.C.  the 
censor  Appius  Claudius  commenced  the  construction  of  the  first 
paved  road,  which  led  from  Rome  to  Capua.  This  road  was 
named  Via  Appia  (Appian  Way),  and  was  later  extended  and 


I 


4  ELEMENTS   OF  HIGHWAY   ENGINEERING 

improved  by  Trajan.  This  marked  the  beginning  of  the  con- 
struction of  Rome's  remarkable  system  of  highways.  During 
the  next  century  Rome  continued  to  flourish,  and  since  the 
roads  were  an  absolute  necessity  for  the  movements  of  troops  to 
the  various  provinces,  the  construction  of  roads  increased  to 
such  an  extent  that  at  the  end  of  200  B.C.  the  total  system 
comprised  about  48,500  miles.  Many  of  the  main  roads  were 
built  under  the  auspices  of  different  rulers  and  bear  their  names. 
Among  these  roads  may  be  mentioned  the  Appian,  Aurelian, 
Flaminian,  and  Domitian  ways.  Twenty-nine  of  these  roads 
led  to  the  capital.  During  the  reign  of  Trajan,  the  Roman 
Empire  reached  its  greatest  magnitude,  comprising  Italy,  Britain, 
Gaul,  Spain,  Western  Germany,  part  of  Asia  Minor  and 
Arabia,  the  northern  part  of  Africa,  and  the  islands  in  the 
Mediterranean. 

It  is  evident  in  examining  the  old  Roman  roads,  very  clear 
traces  of  which  appear  in  many  of  the  European  countries, 
that  directness  of  line  between  two  points  was  a  prime  object. 
A  straight  line  was  attained  many  times  in  spite  of  the  natural 
difficulties  which  had  to  be  overcome.  Tunnels,  bridges,  and 
retaining  walls  remain  as  monuments  to  the  skill  of  the  Roman 
engineers.  The  Flaminian  Way,  in  crossing  the  Apennines, 
passes  through  a  tunnel  about  one  thousand  feet  long;  the 
Appian  Way  near  Ariccia,  for  a  length  of  about  seven  hundred 
and  fifty  feet,  is  constructed  on  a  viaduct,  the  retaining  walls 
of  which  have  a  mean  height  of  43  feet,  while  the  viaduct  con- 
tains three  arch  spans  which  serve  as  a  waterway.  In  low  and 
level  land  the  roads  were  elevated  to  a  considerable  height 
above  the  adjoining  ground. 

Some  of  the  great  military  Roman  roads  were  from  36  to  40 
feet  wide.  The  middle  part,  12  to  16  feet  in  width,  was  gener- 
ally paved  or  surfaced  with  some  suitable  material.  This  part 
of  the  road  is  supposed  to  have  been  used  by  the  infantry. 
On  each  side  of  the  middle  portion  was  built  a  raised  path, 
about  two  feet  wide,  which  may  have  been  used  by  the  officers. 
Beyond  these  paths  on  either  side  was  a  width  of  about  eight 
feet,  which  was  supposed  to  have  been  used  by  the  cavalry. 


6  ELEMENTS   OF  HIGHWAY  ENGINEERING 

The  breadth  of  the  vicinal  roads  was  fixed  by  the  law  of  the 
"Twelve  Tables"  at  8  feet. 

In  constructing  these  roads  two  parallel  furrows,  defining 
the  width  of  the  road,  were  made,  and  the  soil  between  these 
furrows  was  removed  to  such  a  depth  that  a  firm  and  solid 
foundation  was  obtained.  Sometimes  when  the  soil  was  soft, 
it  was  made  more  compact  by  driving  small  piles  into  it.  This 
trench  was  then  filled  up  to  a  certain  height  with  sand,  which 
was  firmly  compacted.  Upon  this  sand-bed  four  successive 
layers  of  masonry  were  built  as  follows: 

1.  The  Statumen,   10  to  20  inches  thick,  formed  of  large 
stones  laid  flat  in  courses  and  bonded  together  with  mortarorclay. 

2.  The  Rudus,  about  eight  inches  thick,  composed  of  rubble 
masonry. 

3.  The  Nucleus,  having  a  thickness  of  10  inches,  built  of 
masonry  similar  to  concrete  and  often  composed  of  fragments 
of  pottery  and  brickbats. 

4.  The  Summa  Crusta,  formed  of  very  hard  materials  bonded 
together  with  a  lime  mortar.     On  many  of  the  military  roads 
large  stones,  bedded  in  the  Nucleus,  were  used  for  this  layer,  while 
on  other  roads  small  stones  mixed  with  mortar  were  employed. 

The  total  thickness  of  the  four  courses  was  about  four  feet. 
All  of  the  roads,  however,  were  not  constructed  according  to 
this  standard.  Some  of  the  roads  that  were  originally  built  of 
sand  or  gravel  were  later  surfaced  with  stones  of  variable  dimen- 
sions. The  Appian  Way  between  Rome  and  Brindisi  for  a 
length  of  about  five  hundred  miles  was  surfaced  with  large 
stones,  cut  into  irregular  shapes,  bedded  very  carefully  in  mortar, 
and  laid,  in  some  cases,  with  very  close  joints.  These  stones, 
3,  4,  and  5  feet  square,  were,  according  to  some  authori- 
ties, transported  more  than  one  hundred  miles  for  use  in  this 
road.  In  many  places  on  the  Domitian  Way  the  surface  was 
paved  with  square  blocks  of  marble.  '  In  others,  the  stones  were 
brought  from  the  fields  and  laid  in  mortar.  Between  Nimes 
and  Beaucaire,  where  the  Roman  road  has  been  found  to  be 
intact  in  places,  it  was  paved  with  dressed  stones  about  seven 
inches  thick.  Excavations  have  shown  in  some  cases  that  the 


HISTORICAL   REVIEW  7 

Statumen  was  replaced  by  broken  stones  of  'variable  size. 
In  other  places  the  Statumen  was  replaced  by  a  layer  of  com- 
pacted earth,  the  Rudus  consisted  of  a  bed  of  lime  mortar, 
and  a  layer  of  broken  stone  replaced  the  Nucleus.  Archaeolo- 
gists have  found  that  old  Roman  streets  within  the  cities  of 
Pompeii  and  Herculaneum  were  paved  with  large  blocks  of  lava. 
They  have  also  unearthed  some  paved  streets  in  which  the 
blocks  of  a  similar  size  to  those  used  to-day  were  laid  on  a 
mortar  bed. 

The  reasons  which  led  to  the  adoption  of  the  different  types 
of  massive  construction  have  not  been  given  by  historians. 
Without  doubt,  the  availability  of  the  materials  influenced 
the  use  of  different  sized  stones  and  the  arrangement  of 
courses.  It  is  not  difficult  to  imagine  that  the  desire  of 
the  rulers  to  leave  behind  some  substantial  monument 
of  their  reign  led  to  the  use  of  some  of  the  methods  adopted. 
The  traffic  certainly  was  not  such  as  to  warrant  the  construction 
of  roads  four  feet  thick.  Chariots  and  carts  on  two  or  four 
wheels,  having  a  width  of  about  five  feet,  were  the  principal 
types  of  vehicles  used.  First  cost  was  probably  of  secondary 
importance,  since  a  large  part  of  the  work  was  done  by  captives 
or  by  the  armies. 

The  care  of  the  roads  was  intrusted  to  a  person  of  high 
rank.  The  office  of  Superintendent  of  Highways,  or  Curator 
Viarum,  as  it  was  then  called,  was  one  of  great  dignity  and 
honor.  Julius  Caesar  was  the  first  of  high  rank  to  occupy  this 
office,  and  after  his  occupancy  the  office  was  rarely  conferred 
upon  any  but  men  of  consular  dignity.  Due  to  the  fact  that 
the  roads  played  such  an  important  part  in  the  development 
of  the  Roman  Empire,  it  is  not  surprising  that  the  memories 
of  Caesar  Augustus,  Vespasian,  Trajan,  and  Domitian  were 
honored,  at  the  order  of  the  Roman  Senate,  by  the  erection  of 
triumphal  arches. 

EARLY  FRENCH  HIGHWAYS.  During  the  year  A.D.  300  the 
wonderful  system  of  roads,  built  up  by  the  Romans  in  Gaul, 
was  abandoned  due  to  the  Barbarian  invasion.  In  395  the 
Roman  Empire  was  divided  into  two  parts,  the  Eastern  and 


8  ELEMENTS   OF   HIGHWAY   ENGINEERING 

the  Western  Empires.  The  Western  Empire  was  finally  de- 
stroyed in  476  and  at  its  downfall  road  building  practically 
ceased.  Since  the  small  amount  of  commercial  traffic  was  ac- 
complished with  pack-animals,  the  highways  outside  the  large 
cities  became  in  time  no  better  than  bridle-paths.  No  care 
was  taken  of  them,  and  the  borders,  as  well  as  the  roadway 
itself,  became  covered  with  small  trees  and  bushes. 

During  the  reign  of  King  Charlemagne,  from  771  to  814, 
some  activity  was  again  shown  in  building  highways,  necessi- 
tated by  his  various  military  expeditions.  The  work  was  done 
by  the  armies  or  by  the  people  whom  he  vanquished.  It  was 
about  950  that  the  streets  of  Cordova,  Spain,  were  supposed 
to  have  been  paved.  After  the  reign  of  Charlemagne,  and  up 
to  A.D.  noo,  conditions  grew  worse.  In  France  the  feudal 
regime  was  inaugurated  and  kingly  rights  were  assumed  by  the 
dukes,  counts,  and  other  titled  personages,  who  set  themselves 
up  as  leaders  of  their  districts.  The  whole  nation  was  dis- 
turbed by  the  internal  wars  resulting  from  the  disputes  of  these 
feudal  chiefs.  It  was  during  this  period  of  petty  wars  that  the 
roads  perhaps  suffered  the  most,  since  at  times  they  were  torn 
up  and  destroyed  as  a  matter  of  defence.  The  social  state  in 
the  Middle  Ages  was  such  that  the  use  of  a  road  as  a  means 
of  communication  was  practically  abandoned.  It  was  not  safe 
for  any  one  to  travel,  since  both  life  and  property  were  at  stake. 
Where  travel  was  possible  the  head  of  each  fief  demanded  toll 
of  the  persons  using  the  road,  the  money  being  used  for  his 
own  private  enterprises.  Since  the  head  of  the  fief  had  absolute 
and  final  authority  in  his  particular  district,  the  tolls  were 
heavy  and  an  extreme  hardship  to  those  who  had  to  pay  them. 
From  noo  to  1200  the  only  road  construction  undertaken  com- 
prised the  opening  of  some  of  the  old  roads  incidental  to  the 
movements  of  troops  in  the  Wars  of  the  Crusades.  The  de- 
plorable conditions,  as  outlined  above,  continued  in  France  until 
the  middle  of  the  thirteenth  century,  at  which  time  a  few  of 
the  roads  leading  from  Paris  to  the  feudal  provinces  in  the  near 
vicinity  were  improved.  This  work  was  generally  done  under 
the  direction  of  the  provincial  chiefs,  and  the  paving  was  ac- 


HISTORICAL  REVIEW  9 

compHshed  in  a  very  primitive  manner.  The  streets  in  the 
City  of  Paris  were  filthy  early  in  the  thirteenth  century. 
On  good  authority  it  is  stated  that  King  Philip  Augustus  was 
so  disturbed  at  the  stench,  when  he  opened  a  window  in  his 
palace  one  day,  that  he  ordered  all  of  the  streets  of  the  city 
to  be  paved  with  stone.  This  improvement  was  not  demanded 
by  the  character  of  the  traffic,  as  it  was  not  until  about  1300 
that  carriages,  the  use  of  which  had  almost  entirely  disappeared, 
again  came  into  vogue.  In  spite  of  various  edicts  issued  by 
royal  proclamation  from  1465  to  1600,  the  feudal  system  and 
the  administrative  organization  of  the  government  were  such 
that  the  revenues,  which  should  have  been  spent  in  maintaining 
the  roads,  were  diverted  to  other  channels.  Roads  of  secondary 
importance  were  not  improved  at  all,  and  the  main  highways, 
except  in  the  vicinity  of  large  cities,  were  not  practicable  for 
use  as  carriageways. 

In  1 66 1,  Colbert,  who  was  Minister  of  Finance  of  France  at 
that  time,  did  much  to  try  and  bring  about  a  change  in  con- 
ditions. In  spite  of  his  far-sighted  policies  with  regard  to  the 
construction  and  maintenance  of  highways,  no  material  progress 
was  made  in  developing  the  French  system  up  to  1700,  with  the 
exception  of  the  construction  of  a  few  roads  near  Paris,  among 
which  were  those  of  Orleans  and  Versailles.  The  construction 
and  maintenance  of  the  French  roads  for  a  long  time  had  been 
generally  carried  out  by  means  of  the  "corvee,"  which  was  a 
system  of  compulsory  labor.  M.  Turgot,  a  minister  of  France, 
recognized  the  injustice  of  this  system  and  suggested  several 
reforms  both  as  to  the  "corvee "  and  the  feudal  systems. 
Although  Turgot  was  bitterly  opposed,  he  succeeded  in  bringing 
about  the  general  abolishment  of  the  "corvee,"  in  1776.  He 
was  supported  and  defended  by  King  Louis  XVI  until  Marie 
Antoinette  took  part  against  her  spouse.  Turgot  was  forced 
to  resign  in  1777,  and  would  have  been  imDrisoned  in  the  Bastille 
if  the  King  had  not  interfered. 

Due  to  the  fact  that  Turgot  had  accomplished  the  abandon- 
ment of  the  "corvee,"  it  became  necessary  to  find  some  method 
of  constructing  the  highways  at  a  greatly  reduced  cost.  This 


10  ELEMENTS   OF   HIGHWAY  ENGINEERING 

problem  was  successfully  overcome  by  Pierre  Marie  Jerome 
Tresaguet,  who  at  this  time  was  chief  engineer  of  the  District 
of  Limoges,  France.  It  was  due  to  his  efforts  and  skill  as  an 
engineer  that  the  first  steps  toward  modern  and  scientific  road- 
building  were  taken.  Tresaguet 's  mode  of  constructing  roads, 
as  described  by  himself  in  1764,  and  adopted  generally  in  France 
in  1775,  was  as  follows: 

"  The  bottom  of  the  foundation  is  to  be  made  parallel  to  the 
surface  of  the  road.  The  first  bed  (of  stones)  on  the  foundation 
is  to  be  placed  on  edge,  and  not  on  the  flat,  in  the  form  of  a 
rough  pavement,  and  consolidated  by  beating  with  a  large 
hammer,  but  it  is  unnecessary  that  the  stones  should  be  even 
one  with  another.  The  second  bed  is  to  be  likewise  arranged 
by  hand,  layer  by  layer,  and  beaten  and  broken  coarsely  with 
a  large  hammer,  so  that  the  stones  may  wedge  together  and  no 
empty  space  may  remain.  The  last  bed,  three  inches  in  thick- 
ness, is  to  be  broken  to  about  the  size  of  a  walnut  with  a  small 
hammer,  on  one  side  on  a  sort  of  anvil,  and  thrown  upon  the 
road  with  a  shovel  to  form  the  curved  surface.  Great  attention 
must  be  given  to  choose  the  hardest  stone  for  the  last  bed,  even 
if  one  is  obliged  to  go  to  more  distant  quarries  than  those  which 
furnish  stone  for  the  body  of  the  road;  the  solidity  of  the  road 
depending  on  this  latter  bed,  one  cannot  be  too  scrupulous  as 
to  the  quality  of  materials  which  are  used  for  it."  He  is  also 
credited  with  being  the  first  to  propose  a  system  of  maintenance. 

The  Revolution  naturally  retarded  the  development  of  the 
national  road  system  of  France.  During  the  period  from  1804 
to  1814,  while  Napoleon  Bonaparte  was  Emperor  of  France, 
road-building  gained  a  new  stimulus.  One  result  was  the  estab- 
lishment of  the  remarkable  system  of  national  roads.  It  is  very 
probable  that  Napoleon's  various  military  expeditions  into  the 
surrounding  countries  furnished  the  motive  for  the  construction 
of  these  roads.  About  this  time  was  created  the  renowned 
Department  of  Roads  and  Bridges,  which  was  given  control  of 
road  construction  in  France. 

EARLY  BRITISH  HIGHWAYS.  Conditions  in  Great  Britain 
after  the  fall  of  Rome  and  during  the  Dark  Ages  were  similar 


HISTORICAL   REVIEW  11 

to  those  in  France.  The  roads  were  allowed  to  falf  into  a  most 
deplorable  state.  An  act  passed  in  England  in  1285  directed 
that  all  bushes  and  trees  should  be  cut  down  for  a  distance  of 
200  feet  on  either  side  of  the  highway.  The  undergrowth  had 
become  so  thick  along  the  highways  that  it  afforded  an  excellent 
hiding-place  for  robbers,  which  led  to  the  improvement  sought 
by  the  above  act. 

The  first  act  for  paving  the  streets  of  London  was  passed  in 
1532,  and  apparently  for  a  somewhat  similar  reason  as  was  the 
case  in  Paris.  In  the  statute,  the  streets  were  described  as 
"very  foul,  and  full  of  pits  and  sloughs,  so  as  to  be  mighty 
perilous  and  noxious,  as  well  for  all  the  king's  subjects  on  horse- 
back, as  on  foot  with  carriages."  Large  irregular  boulders,  6 
to  9  inches  deep,  were  first  used.  Due  to  the  wide  joints  be- 
tween the  stones,  the  irregular  shapes,  and  the  unstable  founda- 
tions, the  surface  soon  became  very  rough. 

In  1555  a  law  was  passed  providing  that  surveyors  should 
be  elected  to  take  charge  of  the  roads  in  their  parishes  and 
empowering  them  each  year  to  exact  four  days'  work  on  the 
roads  from  every  parishioner.  In  1562,  these  supervisors  were 
empowered  to  turn  any  watercourses  or  springs  from  the  high- 
ways to  ditches  on  the  adjoining  ground,  and  were  further  em- 
powered to  repair  a  road  with  material  taken  from  any  source 
with  or  without  the  owner's  permission.  The  first  turnpike 
act  was  passed  in  1663,  but  little  was  done  to  the  roads.  Al- 
though passable,  they  were  in  a  very  poor  condition.  Ruts 
and  mud-holes  4  feet  in  depth  were  of  frequent  occurrence. 
By  1809,  due  to  the  fact  that  the  turnpike  system  had  been 
extended,  there  were  over  one  thousand  turnpike  trusts  to  keep 
the  roads  in  repair.  This  supervision,  however,  was  partially 
restricted  to  small  communities.  It  was  not  until  McAdam 
took  charge  of  the  roads  that  any  systematic  improvement  of 
the  roads  was  accomplished. 

John  Loudon  McAdam  returned  from  America  to  Scotland 
in  1783,  and  was  commissioner  and  trustee  of  roads  in  Scotland 
from  this  time  until  1798.  Minutes  of  evidence  given  by  him 
in  1823  said:  "In  1798  I  began  to  make  it  a  sort  of  business. 


12 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


Without  saying  to  any  one  what  my  object  was,  I  travelled  all 
over  the  country  in  different  parts — as  often  as  I  had  leisure 
and  convenience  down  to  the  time  I  took  charge  of  the  Bristol 
Roads,  or  about  the  latter  end  of  1815.  I  found  that  the  roads 
were  extremely  bad  in  all  parts  of  Great  Britain  as  far  back 
as  1798,  and  that  very  little  improvement  took  place  in  them 
between  then  and  the  year  1815,  which  I  attributed  to  the 
ignorance  of  the  persons  who  had  charge  of  them,  the  ignorance 
of  the  surveyors,  the  total  want  of  science.  I  found  the  ma- 
terials so  applied  that  the  roads  were  all  loose,  and  carriages, 
instead  of  passing  over  the  roads,  plowed  them;  that  was  the 
general  fault  of  the  roads;  and  the  loose  state  of  the  roads, 
I  apprehend,  was  owing  to  the  bad  selection  of  materials,  the 
bad  preparation,  and  the  unskilful  laying  of  them."  McAdam 
was  the  first  to  recommend  the  construction  of  a  broken-stone 
surface  of  small-sized  broken  stone  without  any  foundation 
other  than  that  furnished  by  the  earth  road-bed.  Associated 
with  the  period  in  which  McAdam  demonstrated  the  success 
of  his  method  of  construction  are  the  names  of  several  other 
engineers,  namely,  Telford,  Walker,  and  Edgeworth,  all  of  whom 
helped  further  to  perfect  the  principles  laid  down  by  McAdam 
and  Tresaguet. 

The  boulder  pavements  first  used  in  London  were  later  suc- 
ceeded by  a  crude  type  of  block  pavement  composed  of  blocks 
measuring  6  or  8  inches  across  the  surface.  The  blocks  were 
very  irregular  in  shape,  and  as  no  stable  foundation  was  pro- 
vided, these  pavements  were  no  improvement  on  those  first 
constructed.  It  was  not  until  1824  that  the  deficiencies  of  this 
system  were  pointed  out  by  Telford.  He  recommended  using 
paving  stones  of  granite,  cut  square  on  all  sides,  so  as  to  furnish 
a  close  joint  and  having  a  base  the  same  dimension  as  the  top 
surface.  The  dimensions  of  the  stones  were  to  be  as  follows: 


Class  of  Street 

Width,  Inches 

Depth,  Inches 

Length,  Inches 

For  streets  of  the  1st  class  
For  streets  of  the  2d  class  
For  streets  of  the  3d  class 

6 

5 
4// 

to  7>£ 
i  "    6 

10 

9 
7  to  8 

ii  to  13 
9  "    12 
7  "    ii 

HISTORICAL  REVIEW  13 

He  also  recommended  constructing  the  pavement  on  a  broken- 
stone  foundation  12  inches  deep. 

In  other  parts  of  Europe,  from  the  time  of  Rome's  downfall 
to  about  the  beginning  of  the  eighteenth  century,  the  history 
of  road-building  is  practically  a  repetition  of  the  developments 
during  the  same  period  in  France  and  England.  It  was  not 
until  after  the  influential  work  of  Tresaguet,  McAdam,  Telford, 
and  others  had  been  accomplished  that  any  marked  progress 
in  the  development  and  construction  of  roads  throughout  Europe 
took  place. 

EARLY  AMERICAN  HIGHWAYS.  According  to  existing  rec- 
ords, the  first  highways  constructed  in  America  were  those 
supposed  to  have  been  built  by  the  ancient  Incas  of  Peru. 
Gautier,  in  describing  one  of  these  roads  which  led  from  Quito 
to  Cuzco,  said  the  road  had  a  width  of  25  feet,  and  was  paved 
in  some  places,  where  it  was  necessary,  with  large  stones  10 
feet  square.  The  roadsides  were  bordered  with  trees  and  sup- 
ported in  places  by  retaining  walls. 

The  development  of  highways  in  North  America  was  much 
slower  than  in  other  countries.  As  the  United  States  was  settled 
by  many  colonists  from  England,  at  a  time  when  the  road 
situation  in  England  was  particularly  bad,  the  value  of  im- 
proved highways  was  not  appreciated.  The  colonies  were  estab- 
lished along  the  eastern  coast  at  widely  separated  points.  Most 
of  the  communication  between  the  different  settlements  was 
carried  on  by  water.  Because  the  colonists  were  occupied  in 
protecting  themselves  from  the  Indians,  and  on  account  of  lack 
of  money,  they  did  very  little  in  the  way  of  laying  out  roads 
outside  of  the  settlements,  except  to  clear  out  rough  trails.  It 
is  known  that  some  paving  was  attempted  within  the  settle- 
ments at  a  very  early  date.  The  streets  of  Boston  were  paved, 
probably  with  cobble-stones,  as  early  as  1663. 

Records  show  that  a  similar  form  of  pavement  was  intro- 
duced in  New  York  at  about  the  same  time.  The  following 
rules  were  adopted  by  the  Government  of  New  York  in  1664: 
"The  highways  to  be  cleared  as  folio  we  th,  viz.,  the  way  to  be 
made  clear  of  standing  and  lying  trees,  at  least  ten  feet  broad; 


14  ELEMENTS   OF   HIGHWAY   ENGINEERING 

all  stumps  and  shrubs  to  be  cut  close  by  the  ground.  The 
trees  to  be  marked  yearly  on  both  sides;  sufficient  bridges  to 
be  made  and  kept  over  all  marshy,  swampy,  and  difficult  dirty 
places,  and  whatever  else  shall  be  thought  more  necessary  about 
the  highways  aforesaid." 

The  French,  who  first  settled  hi  Canada,  took  advantage 
of  the  various  great  rivers  and  lakes  on  the  northern  border  of 
the  United  States  and  the  Mississippi  River  and  its  tributaries 
in  establishing  a  line  of  settlements  west  of  the  Allegheny  Moun- 
tains. It  was  evidently  the  intention  of  the  French  to  form  a 
cordon  of  settlements  west  of  those  of  the  English. 

The  only  connections  between  the  French  and  English  set- 
tlements over  land  were  the  various  trails  made  by  big  game 
animals  or  by  the  Indians.  The  buffalo  seemed  to  have  had  a 
peculiar  instinct  in  picking  out  the  easiest  trails.  In  many 
instances  these  trails  were  followed  by  the  Indians,  and  with 
the  progress  of  civilization  they  became  highways. 

The  old  York  road  which  ran  between  New  York  City  and 
Philadelphia  was  the  first  important  highway  in  the  colonies. 
It  was  laid  out  in  1711.  In  forcing  the  French  from  the  Ohio 
Valley  about  the  middle  of  the  eighteenth  century,  several  mili- 
tary expeditions  were  sent  out  from  Virginia  across  the  Alle- 
gheny Mountains.  George  Washington  was  one  of  the  first  to 
lay  out  a  military  road  over  this  route  in  1754,  for  the  purpose 
of  moving  Colonel  Fry's  army.  In  1755,  General  Braddock,  of 
the  English  Army,  in  making  a  similar  expedition  against  the 
French,  followed  somewhat  the  same  route  as  laid  out  by 
Washington.  There  was  very  little  real  progress  in  road-making 
until  the  last  quarter  of  the  eighteenth  century,  when  the  neces- 
sity for  more  and  better  roads  was  met  in  many  cases  by  the 
construction  of  toll  roads  in  various  parts  of  the  country.  These 
roads  were  built  and  owned  by  private  corporations  which 
exacted  payment  from  those  using  them. 

The  old  Lancaster  Turnpike,  which  ran  from  Philadelphia 
to  Lancaster,  Pennsylvania,  was  the  first  broken-stone  road 
built  in  the  United  States.  As  originally  constructed  in  1792, 
the  surface  was  composed  of  stones  of  all  sizes  thrown  together 


HISTORICAL   REVIEW  15 

and  covered  with  earth.  The  roadway  became  very  unsatis- 
factory, and  at  a  later  date  it  was  reconstructed  with  a  broken- 
stone  surface,  no  stones  being  used  in  the  surface  that  would 
not  go  through  a  2-inch  ring.  The  success  of  this  type  of  con- 
struction was  quickly  appreciated,  and  many  of  the  toll  roads 
constructed  up  to  1811  were  built  by  this  method.  By  1811 
there  were  about  4,500  miles  of  highways  comprising  317  turn- 
pikes that  had  been  chartered  in  New  York  and  the  New  England 
States.  Many  of  the  roads  built  by  private  corporations  were 
not  a  financial  success,  and  whenever  abandoned  they  usually 
came  under  the  control  of  the  State  in  which  they  were  located. 
During  the  time  that  toll  roads  were  being  built  to  a  large 
extent,  the  forced  labor  system  was  practically  abandoned.  It 
gradually  returned  with  the  decline  of  the  toll  roads  and  is  still 
in  operation  in  many  of  the  States. 

The  construction  of  the  Cumberland  or  National  Road  by 
the  Government  led  to  some  further  activity  in  road-buildingv 
This  road  extended  from  Washington  westward  to  St.  Louis, 
and  was  built  with  a  2o-foot  width  of  broken  stone,  18  inches 
deep  at  the  middle  and  12  inches  deep  at  the  sides.  It  was 
started  in  1806,  and  various  appropriations  were  made  for  its 
construction  by  Congress  during  a  period  of  over  forty  years. 
In  certain  localities  the  Cumberland  Road  was  built  upon  the 
bed  of  the  road  as  laid  out  previously  by  Washington  and 
Braddock. 

Up  to  1840  the  principal  paving  material  used  in  American 
cities  was  cobble-stone.  The  improvement  of  highways  outside 
of  the  cities  was  retarded,  for  a  period  of  several  years  begin- 
ning with  1837,  due  to  a  money  stringency.  The  rapid  develop- 
ment of  the  railroads  in  this  country  also  served  to  establish 
communication  between  points  which  otherwise  would  have  been 
connected  by  improved  highways. 


CHAPTER  II 

ECONOMICS,  ADMINISTRATION,  LEGISLATION,  AND 
ORGANIZATION 

Since  the  middle  of  the  nineteenth  century  financial  problems 
pertaining  to  the  construction  of  streets  have  been  given  con- 
sideration by  American  municipal  engineers.  It  was  not  until 
about  1890,  however,  that  active  interest  in  the  finances  of  the 
improvement  of  highways  outside  of  built-up  districts  developed 
in  the  United  States.  The  rapid  development  of  the  building 
of  highways  is  shown  by  the  remarkable  increase  in  the  appro- 
priations by  states,  counties,  townships,  and  districts  in  the 
period  from  1904  to  1914.  The  total  appropriations  in  1904 
were  $79,000,000,  while  in  1914  they  reached  the  sum  of  $225,- 
000,000.  Since  1890  marked  progress  has  been  made  in  the 
methods  of  construction,  but  the  economic  problems  of  highway 
engineering  have  not  been  given  the  consideration  by  state  and 
county  highway  departments  which  the  importance  of  the 
subject  demands. 

The  construction  and  maintenance  of  highways  involve  the 
expenditure  of  large  sums  of  money  which  must  eventually  be 
paid  by  the  people.  In  business,  unless  the  capital  invested  is 
protected  by  available  assets  and  unless  it  has  an  earning 
capacity,  the  investment  is  not  considered  a  desirable  one.  To 
apply  this  criterion  to  the  expenditure  of  money  for  highway 
construction  is  difficult,  but  the  same  underlying  principle  should 
be  kept  in  mind.  It  is  impracticable  to  state  the  value  of  good 
roads  in  dollars,  although  statisticians  have  frequently  attempted 
to  show  the  saving  that  would  result  in  the  cost  of  hauling 
various  products  over  improved  surfaces.  Such  figures  may  be 
very  misleading,  since  they  are  based  frequently  on  data  of  a 
meager  nature.  The  return  for  the  capital  invested  will  there- 

16 


ECONOMICS  17 

fore  have  to  be  summed  up  from  the  standpoint  of  the.  advantages 
resulting  from  the  improvement  of  highways. 

BENEFITS  OF  IMPROVED  HIGHWAYS.  The  benefits  which  result 
from  the  construction  of  a  given  highway  naturally  depend  upon 
its  local  environments.  The  improvement  of  highways  outside 
urban  districts  may  or  may  not  result  in  identical  benefits  to 
the  communities  in  which  they  are  respectively  located.  In 
the  enumeration  of  the  advantages  resulting  from  the  develop- 
ment of  good  roads  and  streets,  it  is,  therefore,  evident  that  in 
general  only  a  group  of  the  benefits  mentioned  will  result  from 
the  improvement  of  a  specific  highway.  The  advantages  and 
benefits  of  good  highways  are  set  forth  in  the  following  list, 
but  not  in  relational  order  based  on  their  value,  since  such 
rating  will  vary  with  individual  highways. 

1.  Development  of  commerce. 

2.  Development  of  industries. 

3.  Development  of  agriculture. 

4.  Development  of  natural  resources. 

5.  Development  of  intellectual  and  social  life. 

6.  Improved  appearance  of  roads  and  streets. 

7.  Permanency  of  alignment  and  grade  of  highways. 

8.  Decrease  in  cost  of  transportation. 

9.  Development  of  methods  of  transportation. 

10.  Facilitation  of  travel. 

11.  Development  of  tourist  travel. 

12.  Improvement  of  sanitary  conditions. 

13.  Increase  in  land  values. 

14.  Increase  in  fire  protection. 

15.  Increase  in  rural  population. 

1 6.  Development  of  rural  free  delivery. 

It  is  apparent  that  many  of  these  advantages  cannot  be  esti- 
mated on  a  money  basis.  Although  the  surfacing  will  wear  out 
in  time,  many  of  the  advantages  resulting  from  the  original 
improvement  are  permanent,  and  under  proper  methods  of  finan- 
cing, the  cost  would  not  be  considered  out  of  proportion  to  the 
benefits  derived. 

FINANCING  HIGHWAYS.     The  systems  of  financing  the  con- 


18  ELEMENTS   OF  HIGHWAY  ENGINEERING 

struction  and  maintenance  of  highways  in  the  United  States 
will  be  considered  under  the  following  heads: 

1.  Labor  tax. 

2.  Convict  labor. 

3.  Direct  taxation. 

4.  Direct  appropriation. 

5.  Bond  issues. 

6.  Private  subscriptions. 

Labor  Tax  System.  The  labor  tax  system  permits  the  pay- 
ment of  highway  taxes  in  labor  instead  of  cash.  This  system 
was  extensively  used  in  the  United  States  in  the  development 
of  highways  outside  of  built-up  districts  until  1890.  Although 
it  is  being  rapidly  abolished  in  many  sections,  nevertheless  sta- 
tistics show  that  in  1914  the  system  was  in  use  in  twenty-one 
states.  Little  good  can  be  expected  from  such  a  system,  since 
interest  and  earnestness  of  effect  are  generally  lacking.  The 
work  is  usually  done  at  times  which  suit  the  convenience  of 
those  that  perform  it  rather  than  at  times  which  would  be  ad- 
vantageous from  the  standpoint  of  the  improvement  of  the 
highways.  Of  course  work  done  by  this  method  is  generally 
better  than  none  at  all,  but  it  is  realized  that  the  expenditure 
of  an  equivalent  sum  of  money  under  intelligent  administration 
will  produce  better  and  more  far-reaching  results.  There  are 
instances  where  results  accomplished  by  this  method  have  been 
very  satisfactory,  as,  for  example,  the  excellent  work  done  with 
road  drags  on  the  highways  in  different  parts  of  the  country, 
particularly  in  connection  with  the  maintenance  of  earth  roads. 

Convict  Labor.  Since  1910  the  utilization  of  convicts  in 
connection  with  the  construction  of  roads  has  received  consider- 
able attention  in  many  parts  of  the  United  States.  The  use 
of  convicts  for  this  purpose  is  not,  however,  of  recent  origin, 
as  they  were  used  in  the  construction  of  the  ancient  highways 
of  Rome  and,  throughout  the  Middle  Ages,  on  highways  in 
other  parts  of  Europe.  The  sociological  and  economic  prob- 
lems involved  are  many.  It  has  been  affirmed  by  various  au- 
thorities that  convict  work  on  highways  must  comply  with  the 
following  conditions:  "(i)  It  must  not  compete  with  outside 


ECONOMICS  19 

free  labor;  (2)  it  must  be  a  benefit  to  the  convict  himself;  (3) 
it  must  be  a  benefit  to  the  state;  (4)  it  must  provide  the  means 
to  rehabilitate  the  convict  in  society  after  his  release  or  at  least 
partially  to  sustain  his  family  and  dependents  during  his  im- 
prisonment. 

"The  evidence  available  indicates  the  advisability  of  follow- 
ing the  honor  system  for  the  good  of  both  the  convict  and  the 
state.  The  privileges  given  should  be  such  as  to  make  road 
work  the  goal  of  the  prisoners'  endeavors.  These  privileges 
should  be:  (i)  absence  of  guns  and  chains;  (2)  substitution 
of  plain  uniform  for  stripes;  (3)  commutation  of  sentence;  (4) 
better  food;  (5)  a  wage;  (6)  freedom  after  work  hours."51 

The  following  conclusions  have  been  derived  from  an  ex- 
haustive study  of  the  use  of  convict  labor  on  highways  in  northern 
parts  of  the  United  States:  "(i)  The  system  can  be  successfully 
applied  under  varying  conditions  of  climate,  location,  and  class 
of  prisoners;  (2)  as  far  as  possible  the  honor  system  should  be 
used  and  commutation  of  sentence  allowed;  (3)  the  choice  of 
convicts  for  honor  road  work  should  be  based  upon  tempera- 
mental fitness  rather  than  upon  nature  of  crime  and  length  of 
term,  but  acceptance  should  be  voluntary  on  the  part  of  the 
prisoner  and  dependent  on  his  satisfactory  physical  condition; 
(4)  of  all  kinds  of  convict  employment,  that  on  the  highways 
should  be  most  attractive  in  wages  and  privileges;  (5)  a  wage 
should  be  paid  not  to  exceed  the  net  earnings  of  the  prisoner; 
(6)  accurate  data  should  be  kept  to  show  all  unit  costs,  together 
with  the  engineer's  estimates  of  the  amount  and  value  of  the 
work  done;  (7)  the  prisoners  should  be  under  the  prison  repre- 
sentatives acting  as  foremen,  and  construction  work  should  be 
under  the  highway  department  representatives  acting  as  engi- 
neers; (8)  concrete  bridge  work,  grading,  and  drainage  present 
a  very  useful  form  of  work  and  should  be  generally  employed."* 

Direct  Taxation.  In  many  communities  a  certain  part  of 
the  general  tax  is  assessed  as  a  highway  tax  to  be  used  both 

*  Sydney  Wilmot,  in  1913  Thesis,  Graduate  Course  in  Highway  Engineer- 
ing at  Columbia  University,  Proceedings  of  the  Academy  of  Political  Science, 
January,  1914. 


20  ELEMENTS   OF  HIGHWAY   ENGINEERING 

for  the  construction  and  maintenance  of  the  highways.  It  is 
generally,  however,  of  such  small  amount  in  rural  districts  that 
very  little  new  construction  can  be  accomplished.  In  order  to 
further  the  construction  of  new  highways,  several  states  levy  a 
tax  for  this  purpose  on  the  abutting  property,  which  pays  in 
part  for  the  cost  of  new  construction.  Such  a  system  is  thought 
to  be  an  equitable  one  in  some  localities.  In  districts  where 
there  are  large  areas  between  the  highways  the  amount  of  tax 
is  varied,  depending  upon  the  distance  of  the  property  from 
the  highway.  One  advantage  of  the  direct  tax  is  that  future 
indebtedness  is  obviated.  The  highway  work  in  many  of  the 
cities  of  the  United  States  is  carried  on  by  some  form  of  special 
assessment.  While  in  some  cases  the  entire  cost  of  grading  is 
paid  by  the  city,  there  are  a  few  instances  where  the  city  pays 
a  certain  per  cent  of  this  cost.  The  same  general  scheme  is  also 
carried  out  in  the  original  construction  of  pavements  and  in 
repaving  work.  An  examination  of  Table*  No.  i  will  show 
the  practice  as  followed  in  several  American  cities.  The  amount 
of  assessment  is  based  on  the  frontage  of  the  property  on  the 
street,  the  total  area,  or  a  combination  of  the  frontage  and  the 
area.  The  frontage  rule  is  more  commonly  used  than  either 
of  the  others.  In  some  cases  the  amount  assessed  is  due  on 
completion  of  the  work.  In  others,  however,  the  amount  is 
paid  in  several  equal  annual  installments,  deferred  payments 
bearing  interest.  The  charter  of  New  York  City  was  amended 
in  1910,  with  reference  to  the  paving  and  repaving  of  streets 
and  the  method  of  payment  therefor,  to  read  as  follows: 

"Street  pavements  shall  be  divided  into  two  classes,  namely: 
Class  'A,'  or  permanent  pavements,  and  Class  'B,'  or  preliminary 
pavements.  Class  'A'  shall  include  all  pavements  of  sheet  asphalt, 
asphalt  block,  wood  block,  granite  block,  or  other  materials  that 
shall,  from  time  to  time,  be  designated  for  this  class  by  the 
Board  of  Estimate  and  Apportionment.  Class  'B'  shall  include 
all  pavements  of  bituminous  macadam  and  such  other  pave- 
ments that  shall  from  time  to  time  be  designated  for  this  class 

*  See  Transactions,  Am.  Soc.  C.  E.f  Vol.  XXXVIII,  pages  336-342. 


ECONOMICS 


21 


TABLE  No.  1  • 

APPORTIONMENT  OF  COST  OF  PAVEMENTS  IN  FIFTY  CITIES 


LOCALITY 

Grading 
Percent 
Paid  by 

Original 
Paving  Percent 
Paid  by 

Repaying 
Percent 
Paid  by 

3£      **« 

City 

Prop- 
erty 

City 

Prop- 
erty 

City 

Prop- 
erty 

City 

i.  Alabama  
*  2.  Arkansas  
3.  California  .... 
4.  Connecticut  .  . 

5- 
6.  Dist.of  Colum. 
7.  Delaware  

Montgomery  .  . 
Little  Rock  .  .  . 
San  Francisco  . 
Hartford  
New  Haven.  .  . 
Washington.  .  . 
Wilmington  .  .  . 
Jacksonville.  .  . 
Atlanta 

50 
IOO 
100 

50 

50 

IOO 
IOO 
IOO 
IOO 

50 

IOO 

50 
"d 

IOO 
IOO 

25 

IOO 
IOO 

c 

IOO 
IOO 

50 

IOO 

d 

2C 

c 

IOO 
IOO 

c 

IOO 

5oc 

IOO 

c 

50 
IOO 
IOO 

67 

a 

5° 
67 

50 

IOO 
IOO 
IOO 
IOO 
IOO 

75 

IOO 

IOO 
IOO 
IOO 
IOO 
IOO 
IOO 

IOO 
IOO 
IOO 
IOO 
IOO 
IOO 
IOO 
IOO 

98 

IOO 
IOO 
IOO 
IOO 
IOO 

IOO 
IOO 

IOO 
IOO 

50 

33 

IOO 
IOO 

50 

33 

50 
"d 

c 

25 

IOO 

50 
IOO 

b 

50 
67 
50 

IOO 
IOO 

IOO 

75 

50 

IOO 
IOO 

IOO 
IOO 

50 

33 

50 

'd 

IOO 
IOO 

25 

IOO 
IOO 
IOO 
IOO 
IOO 

c 
c 

c 

IOO 
IOO 

d 

50 

IOO 

2C 

c 

IOO 

50 

IOO 

IOO 

c 

IOO 

c 

IOO 
IOO 

8.  Florida  

9    Georgia 

10.         " 

Augusta  
Peoria  
Indianapolis.  .  . 
Burlington.  .  .  . 
Topeka  
Louisville  
New  Orleans  .  . 
Portland  
Baltimore  
Lowell  
Springfield  .... 
Worcester  
Detroit  
Minneapolis.  .  . 
St.  Paul  ...... 
Kansas  City.  .  . 
St.  Louis  
Omaha  

50 

IOO 
IOO 

IOO 

75 

IOO 
IOO 

IOO 
IOO 

IOO 
IOO 

50 

IOO 
IOO 
IOO 
IOO 
IOO 
IOO 
IOO 
IOO 

98 

IOO 
IOO 
IOO 

IOO 
IOO 

IOO 

50 

IOO 
IOO 

ii.  Illinois  
12.  Indiana 

13.  Iowa  
14.  Kansas          .  . 

15.  Kentucky.  .  .  . 
1  6.  Louisiana  .... 
17.  Maine  
1  8.  Maryland.  .  .  . 
19.   Massachusetts 

20. 
21. 

22.  Michigan  

IOO 
IOO 
IOO 

c 
c 

c 

IOO 

"d 

2C 

c 

IOO 
IOO 
IOO 
IOO 
IOO 
IOO 

IOO 
IOO 

50 

IOO 

IOO 
IOO 

98 

IOO 
IOO 
IOO 

23.  Minnesota.  .  .  . 
24.                      .... 
25.  Missouri  

26.          "         

27.  Nebraska  .... 
28.  New  Hmpshre 
29.  New  Jersey.  .  . 
30. 
31.  New  York...  . 
32. 
33- 
34- 
35- 
36. 
37-  Ohio  
38.      "     
39.  Oregon.  .  .  ^.  .  . 
40.  Pennsylvania  . 
41. 
42. 
43.  Rhode  Island. 
44.  South  Carolina 
45.  South  Dakota. 
46.  Tennessee  .... 
47.  Utah 

Manchester  .  .  . 
Newark  
Paterson  
Albany 

Brooklyn  
Buffalo  
New  York  .... 
Rochester  
Syracuse  
Cincinnati  .... 
Dayton  
Portland  
Harrisburg.  .  .  . 
Philadelphia.  .  . 
Scranton  
Providence  .... 
Charleston.  .  .  . 
Sioux  Falls.  .  .  . 
Nashville  
Salt  Lake  
Richmond  .... 
Seattle  

IOO 
IOO 

c 

IOO 

c 

IOO 

c 

50 

IOO 
IOO 
IOO 

48.  Virginia 

49.  Washington.  .  . 
50.  Wisconsin.  .  .  . 

Milwaukee.  .  .  . 

a  i  sq.  yd.  for  each  front  foot;  city  remainder.      b  3  K  sq.  ft.  for  each  front  foot;  city  re- 
mainder,   c  City  pays  for  street  intersections,     d  City  does  not  pay  for  street  intersections. 


22  ELEMENTS   OF  HIGHWAY   ENGINEERING 

by  the  Board  of  Estimate  and  Apportionment.  No  street,  or 
portion  thereof,  that  shall  have  been  paved  with  class  'A'  pave- 
ment shall  be  repaved  at  the  expense  of  the  adjoining  property- 
owners,  unless  a  majority  of  the  owners  of  the  property  on  the 
line  of  the  proposed  improvement  shall  petition  for  such  repaving 
at  their  expense  by  assessment. 

"Whenever  a  street  paved  with  class  'B'  pavement  shall  be 
repaved,  the  repaving  shall  be  done  with  class  'A'  pavement, 
unless  owners  of  property  on  the  line  of  the  proposed  improve- 
ment petition  the  local  board  having  jurisdiction  for  a  second 
class  'B'  pavement,  to  be  laid  at  the  expense,  by  assessment,  of 
the  adjoining  property-owners,  and  in  such  event  second-class 
'B'  pavement  shall  be  laid  if  said  local  board  so  orders,  and 
the  Board  of  Estimate  and  Apportionment  consents.  When- 
ever a  class  'A'  pavement  shall  be  laid  to  replace  a  class  'BJ 
pavement  that  has  been  laid  at  the  expense  of  the  property- 
owners  by  assessment  there  shall  be  deducted  from  the  cost 
of  such  improvement  the  cost  of  the  class  'B'  pavement,  and 
the  difference  shall  be  paid  by  assessment  upon  the  adjoining 
property,  and  the  amount  equal  to  the  cost  of  said  class  'B' 
pavement  shall  be  borne  and  paid  by  the  city.  But  in  no  case 
shall  the  cost  of  a  second  or  additional  class  'B'  pavement  be 
so  deducted  from  the  amount  to  be  assessed  for  the  laying  of  a 
permanent  or  class  'A'  pavement. 

"The  class  of  the  original  pavement  of  any  street  shall  in 
all  cases  be  determined  by  the  local  board  having  jurisdiction 
and  the  Board  of  Estimate  and  Apportionment." 

Another  form  of  direct  taxation  is  the  licensing  of  motor 
vehicles.  The  money  received  in  license  fees  for  both  vehicles 
and  operators  and  the  money  received  from  penalties  and  fines 
imposed  for  non-observance  of  the  laws  as  a  rule  are  usually 
paid  into  the  state  treasuries  to  be  used  for  the  maintenance  of 
highways.  In  1914  the  revenue  collected  in  New  York  State 
from  this  source  amounted  to  $1,530,000,  and  in  the  State  of 
California  to  $1,340,000. 

Direct  Appropriation.  When  payment  for  highway  improve- 
ment is  made  from  the  general  taxes  of  a  community,  the  ex- 


ECONOMICS  23 

pense  is  borne  by  all  the  people  residing  therein.  A  large  amount 
of  the  state  highway  work  is  paid  for  on  this  basis.  In  many 
municipalities  and  towns  an  amount  sufficient  to  cover  the  cost 
of  the  highway  improvement  is  made  an  item  of  the  annual 
budget. 

Bond  Issues.  Due  to  the  large  sums  of  money  required 
where  extensive  construction  is  contemplated,  the  revenue 
available  from  the  general  taxes  will  not  usually  meet  the 
expense  of  the  improvement.  In  such  cases  it  has  become 
common  procedure  to  issue  bonds,  bearing  interest  from  2%  to 
6  per  cent,  which  are  redeemable  at  different  periods.  The 
amount  of  bonds  issued  should  never  be  out  of  proportion  to 
the  taxable  wealth  of  the  corporate  body  issuing  them.  The 
yearly  cost  of  the  bonds  will  be  the  sum  of  the  amount  which 
will  have  to  be  paid  out  in  interest  and  the  amount  which  will 
have  to  be  set  aside  as  a  sinking  fund  to  redeem  the  bonds. 
The  issuance  of  bonds  renders  a  large  sum  of  money  available 
for  immediate  use  and  extends  the  repayment  over  a  long  period 
of  years.  If  the  term  of  the  bonds  is  made  so  long  that  the 
highways  are  worn  out  before  the  bonds  are  redeemed  and  no 
provision  made  either  for  the  maintenance  of  the  highways  or 
for  the  redemption  of  the  bonds,  a  very  unfortunate  financial 
situation  arises.  To  illustrate  this  point  the  following  case  was 
cited  by  Clifford  Richardson,  M.  Am.  Soc.  C.  E.: 

"It  appears  from  the  Report  of  the  Register  of  Deeds  of  the 
County  of  ...  that  in  1870  it  issued  bonds  for  $300,000  to  run 
for  twenty  years  bearing  6  per  cent  interest.  For  twenty  years 
the  community  paid  annually  $18,000  interest  on  this  loan. 
When  the  bonds  became  due  in  1890,  $360,000  interest  had  been 
paid,  but  no  provision  had  been  made  for  retiring  the  principal. 
It  was  therefore  necessary  to  issue  $300,000  in  bonds  payable 
after  another  thirty  years,  and  at  a  like  rate  of  interest,  to  take 
up  the  first  series.  By  1920,  when  these  bonds  become  due, 
$900,000  in  interest  will  have  been  paid  thereon,  and  the  county 
will  still  owe  the  amount  borrowed."  Richardson  further  states 
that  "as  the  life  of  a  well-constructed  road  may  be  looked  upon 
as  being  between  ten  and  fifteen  years  a  community  which 


24  ELEMENTS   OF  HIGHWAY  ENGINEERING 

issues  bonds  of  this  type  (to  run  for  ten  to  fifteen  years),  with 
the  proper  provision  for  sinking  fund,  cannot  be  considered  to 
have  done  anything  unreasonable,  especially  in  view  of  the  fact 
that  the  improvement  in  the  value  of  adjacent  property  by  the 
construction  of  good  roads  and  the  consequent  increase  in  its 
taxable  value,  may  more  than  meet  the  demands  of  the  sinking 
fund  and  interest.  The  bonds  would  be  paid  for  and  the  debt 
wiped  out  during  the  life  of  the  road,  and  the  cost  of  the  latter 
would  be  the  amount  paid.  There  would  be  no  further  re- 
sponsibility incurred. 

"It  would  be  very  different,  however,  if  bonds  were  issued 
for  forty-one  years.  .  .  .  The  bill  provides  that  bonds  shall  be 
issued  by  the  State  at  4  per  cent  interest  for  a  term  of  forty-one 
years.  The  money  thus  obtained  shall  be  loaned  to  the  various 
counties  in  the  State  for  highway  construction  at  an  interest 
of  5  per  cent,  4  per  cent  of  which  shall  be  devoted  to  payment 
of  interest  on  the  bonds  and  i  per  cent  devoted  to  a  sinking 
fund,  which  would  retire  the  bonds  at  maturity.  On  its  face 
this  is  a  satisfactory  proposition  for  meeting  indebtedness,  but 
the  viciousness  lies  in  the  fact  that  the  roads'  surfaces,  which 
might  be  constructed  with  such  funds,  would  have  been  worn 
out  and  have  disappeared  after  not  more  than  fifteen  years. 
The  State  and  counties  would  then  have  no  roads  and  the 
original  cost  of  constructing  them  would  still  be  a  debt  extend- 
ing for  a  period  of  twenty-six  years.  It  would  be  again  necessary 
to  borrow  money  by  bonds  of  the  same  description  to  build 
new  roads." 

Nelson  P.  Lewis,  M.  Am.  Soc.  C.  E.,  in  making  a  report  to 
the  Board  of  Estimate  and  Apportionment  of  New  York  City, 
advisedly  pointed  out  that  "The  term  of  bonds  issued  for  re- 
paving  should  be  no  longer  than  the  probable  life  of  the  pave- 
ment, or  still  better,  the  funds  for  repaving  should  be  included 
in  the  annual  budget  and  the  city's  borrowing  capacities  reserved 
for  other  purposes." 

Private  Subscription.  There  are  a  few  instances  where  high- 
ways have  been  built  by  private  subscription.  The  largest 
undertaking  of  this  kind  is  the  Coleman  du  Pont  Road  in  Dela- 


ADMINISTRATION  AND   LEGISLATION  25 

ware.  There  have  been  several  roads  constructed  throughout 
the  country,  however,  by  private  capital  as  a  business  enterprise. 
These  roads  after  construction  were  operated  as  toll  roads,  but 
most  of  them  have  been  taken  over  by  the  States  through  which 
they  pass  and  converted  into  public  highways. 


ADMINISTRATION  AND  LEGISLATION 

There  is  a  marked  difference  between  the  systems  of  ad- 
ministration regulating  highway  improvement  in  Europe  and  in 
the  United  States.  In  Europe  the  construction  and  maintenance 
of  highways  outside  of  the  large  cities  in  many  instances  is 
regulated  and  controlled  by  the  national  government,  and  where 
the  government  does  not  build  national  highways,  a  national 
board  may  exist  having  control  in  certain  matters.  Another 
very  pertinent  fact  is  that  European  administration  is  in  the 
hands  of  experienced  engineers.  In  the  United  States  there  is 
no  national  system  of  highways,  each  State  acting  independently 
in  this  matter.  Within  many  States  the  same  lack  of  centraliza- 
tion of  authority  is  found  in  the  highway  work  undertaken  by 
the  various  counties  and  towns.  The  administration  of  the 
state,  county,  and  town  highways  is  vested  in  boards  or  com- 
missions composed  of  several  men,  or  else  the  authority  rests 
in  the  hands  of  one  man.  Unfortunately,  in  the  majority  of 
instances,  these  men  are  not  engineers.  Although  it  is  neces- 
sary to  employ  an  engineering  organization  to  carry  out  the 
work,  some  of  the  work  is  not  done  on  sound  engineering  princi- 
ples, due  to  interference  by  the  lay  bodies.  Moreover,  a  great 
deal  of  the  money  spent  for  construction  and  maintenance  is 
wasted  because  of  the  lack  of  centralization  of  control.  The 
different  systems  of  a  few  of  the  principal  countries  of  the  world 
will  be  described  which  are  typical  illustrations  of  general 
practice. 

FRANCE.  In  France  the  highways  are  classified  as  routes 
nationales  (national  roads) ,  routes  departemen tales  (departmental 
roads),  and  chemins  vicinaux  (vicinal  roads).  The  chemins  vici- 
naux  are  divided  into  several  subsidiary  classes :  chemins  vicinaux 


26  ELEMENTS   OF   HIGHWAY   ENGINEERING 

de  grande  communication  (roads  of  great  importance),  chemins 
d'interet  commun  (roads  of  common  interest),  and  chemins 
vicinaux  ordinaire  (roads  of  little  importance).  Jean  de  Pulligny, 
M.  Am.  Soc.  C.  E.,  states  that,* 

"For  many  years  the  tendency  in  all  departements  has  been 
to  have  only  one  class  of  roads,  the  chemins  de  grande  com- 
munication. No  more  chemins  d'interet  commun  are  created, 
and  every  year  some  routes  departemen tales  drop  from  the 
official  lists  and  they  are  thence  counted  as  chemins  de  grande 
communication.  The  length  of  the  routes  departementales  has 
thus  fallen  from  29,500  miles  in  the  year  1869  to  8,100  at  the 
present  time.  On  January  i,  1911,  the  road  mileage  in  France 
was  as  follows:  Routes  nationales,  24,000  miles;  routes  departe- 
mentales, 8,100  miles;  chemins  vicinaux,  395,700  miles. 

"All  of  the  routes  nationales  are  constructed  and  maintained 
by  the  central  government  under  the  direction  of  the  Departe- 
ment  National  des  Fonts  et  Chaussees,  the  organization  of  which 
is  as  follows:  The  inspecteurs  generaux,  all  of  whom  must  reside 
in  Paris,  are  of  two  grades.  Those  of  the  first  grade  form  a 
permanent  board  of  which  the  ministre  de  travaux  publics  is 
the  nominal  president.  The  board  is  actually  presided  over  by 
a  vice-president,  an  inspecteur-general  who  is  appointed  by  the 
ministre.  This  permanent  board  is  augmented  by  half  of  the 
inspecteurs  generaux  of  the  second  class,  each  half  serving  six 
months.  The  board  has  direct  control  of  all  the  work  of  the 
Departement  des  Fonts  et  Chaussees  in  France.  Besides  the 
care  of  the  routes  nationales  the  Departement  has  under  its 
supervision  all  improvements  in  connection  with  the  bridges, 
rivers,  canals,  harbor  improvements,  the  control  of  the  rail- 
roads, and  attached  services  in  the  colonies. 

"The  board  assigns  inspecteurs  generaux  of  the  second  class 
to  special  fields  of  inspection  covering  the  work  of  several  inge- 
nieurs-en-chef,  and  may  in  very  important  cases  designate  an 
inspecteur-general  of  the  first  class.  The  ingenieurs-en-chef  who 

*  From  1912-1913  Lecture  by  M.  Pulligny,  Ingenieur  en  Chef,  Departe- 
ment des  Fonts  et  Chaussees  de  France,  in  the  Graduate  Course  in  Highway 
Engineering  at  Columbia  University. 


ADMINISTRATION  AND   LEGISLATION  27 

have  charge  of  several  lines  of  work  may  thus 'be  subject  to 
orders  from  a  number  of  inspecteurs-generaux.  The  remainder 
of  the  organization  comprises  ingenieurs  ordinaires,  sous  inge- 
nieurs,  conducteurs  principaux,  conducteurs,  commis  principaux, 
commis  and  commis  stagiaires.  The  title  ingenieur  ordinaire 
is  conferred  on  men  at  the  time  of  their  graduation  from  L'Ecole 
Nationale  des  Fonts  et  Chaussees.  Sous-ingenieurs,  conducteurs, 
and  commis  are  not  graduates  of  the  national  school  and  are 
not  eligible  to  the  grade  of  Ingenieur  des  Fonts  et  Chaussees." 

Pulligny  also  says  that  " France  is  divided  into  eighty-six 
territorial  units  called  Departements.  Each  French  Departe- 
ment  is  also  a  unit  for  several  public  services  and  it  is  a  political 
unit.  It  has  a  governor,  called  a  prefet,  appointed  by  the  central 
government,  and  an  elective  body,  called  conseil  general. 

"All  of  the  chemins  vicinaux  within  a  Departement  are  man- 
aged by  the  prefet  of  that  Departement  and  the  necessary  ex- 
penditures are  appropriated  by  the  conseil  general.  The  direct 
charge  of  the  work  is  in  the  hands  of  a  centralized  body  of 
competent*  technical  men.  In  about  one-half  of  the  Departe- 
ments the  work  is  intrusted  by  the  conseils  generaux  to  the 
body  of  government  engineers  who  are  graduates  of  L'Ecole 
Nationale  des  Fonts  et  Chaussees.  In  forty-six  of  the  French 
Departements  special  technical  bodies  under  a  chief  road  engineer 
have  been  organized  to  look  after  the  work. 

"Each  Departement  is  divided  into  four  or  five  political  dis- 
tricts headed  by  a  sous-prefet  and  called  an  arrondissement. 
In  each  capital  of  these  districts  resides  a  district  road  engineer 
who  works  under  the  direction  of  the  chief  road  engineer,  having 
charge  of  all  the  chemins  vicinaux  of  the  arrondissement.  Each 
arrondissement  is  divided  into  four  or  five  judicial  districts, 
named  Cantons,  having  also  their  small  capitals.  An  assistant 
road  engineer,  acting  under  the  direction  of  the  district  road 
engineer,  looks  after  all  the  chemins  vicinaux  in  the  Canton. 
Finally,  all  the  roads  in  the  Canton  are  divided  into  sections  a 
few  miles  long,  and  in  each  of  these  sections  works  constantly 
the  celebrated  French  cantonnier  or  road  patrolman,  whom  all 
the  motorists  have  noticed  with  his  pickaxe,  shovel,  broom,  and 


28  ELEMENTS   OF   HIGHWAY   ENGINEERING 

wheelbarrow.  These  cantonniers  are  under  the  orders  of  the 
assistant  road  engineer.  A  few  of  them,  who  have  a  shorter 
section,  look  after  the  work  of  their  neighbors,  and  are  called 
chefs  cantonniers. 

"The  cantonniers  are  simple  laborers,  generally  of  agricultural 
training,  and  no  special  knowledge  is  required  of  them  to  enter 
the  service.  They  are  only  expected  to  act  with  respectable 
behavior,  to  be  able  to  read  and  write,  and  to  be  steady,  trust- 
worthy workers.  All  the  members  of  the  road  service,  from  the 
patrolmen  to  the  chief  engineer,  work  under  a  civil  service  law. 
When  they  have  once  entered  the  service  they  can  only  be  dis- 
missed in  case  of  serious  misbehavior.  They  are  promoted  to 
a  better  pay  at  regular  intervals,  and  when  they  retire  after 
thirty  years  of  work  they  receive  an  old-age  pension.  The 
district  engineers  are  generally  chosen  from  the  most  able  and 
experienced  assistant  engineers  who  have  been  in  the  service 
for  many  years.  The  chief  engineer  of  the  Departement  may 
have  been  previously  a  district  engineer,  but  it  is  not  obligatory. 
In  some  cases  he  formerly  was  a  civil  engineer,  a  graduate  from 
one  of  our  principal  schools,  or  an  architect,  or  an  Ingenieur 
des  Fonts  et  Chaussees." 

GERMANY.  The  highways  of  Germany  are  under  the  con- 
trol of  the  different  States  forming  the  Empire.  The  various 
provinces  within  the  States  receive  state  aid  for  the  construction 
of  main  roads.  In  Prussia  the  work  is  generally  supervised  by 
the  Minister  of  Public  Works.  The  direct  administration,  how- 
ever, is  in  the  hands  of  the  provincial  authorities,  who,  in  turn,, 
can  transfer  authority  to  smaller  communal  bodies,  such  as  dis- 
tricts and  parishes.  In  Saxony  the  State  is  divided  into  four 
divisions,  each  one  of  which  is  supervised  by  an  executive  officer 
of  the  Department  of  the  Interior.  The  four  divisions  are 
further  subdivided  into  twenty-seven  districts,  the  work  in  each 
district  being  administered  by  important  executive  officers.  The 
actual  work  of  construction  and  maintenance  throughout  the 
Empire  is  in  the  hands  of  carefully  trained  technical  men. 

GREAT  BRITAIN.  In  Great  Britain  two  classes  of  highways 
are  generally  recognized,  namely,  main  and  district  roads.  The 


ADMINISTRATION   AND    LEGISLATION  29 

classification,  however,  is  not  very  satisfactory,  as  there  are 
main  roads,  which  carry  only  local  traffic,  and  in  some  parts 
there  are  principal  trunk  roads,  which  are  classified  as  district 
roads.  The  highway  administration  is  in  the  hands  of  county 
councils,  which  have  the  care  of  the  main  or  county  roads,  and 
district  councils,  urban  and  rural,  which  have  the  care  of  the 
remainder  of  the  public  highways.  The  cost  of  the  work  is 
paid  for  by  the  taxpayers  residing  in  the  counties  and  districts, 
assisted  by  grants  from  the  Imperial  Exchequer.  One  very  ad- 
mirable feature  of  the  British  system  of  administration  is  the 
power  given  the  Local  Government  Board  relative  to  the  bor- 
rowing capacity  of  a  county  or  district  council.  Before  either 
can  borrow  money  for  highway  improvement  it  must  satisfy 
the  following  regulations  of  the  Local  Government  Board: 

The  sum.  borrowed  shall  not  exceed  at  any  time,  including 
all  outstanding  loans,  the  assessable  value  for  two  years  of  the 
district.  Where  it  exceeds  the  assessable  value  for  one  year, 
the  Board  does  not  give  its  sanction  until  one  of  its  inspectors 
has  held  a  local  inquiry.  The  repayment  of  the  money  bor- 
rowed must  be  made  within  a  certain  time  fixed  by  the  length 
of  life  of  the  proposed  work. 

In  1909  an  act  was  passed  by  Parliament  creating  the  Road 
Board  of  England,  composed  of  five  men.  This  Board  was  ap- 
pointed for  the  purpose  of  improving  the  facilities  for  highway 
traffic  in  the  United  Kingdom.  The  Road  Board,  with  the  ap- 
proval of  the  Treasury,  has  the  power  to  make  advances  to 
county  councils  and  other  highway  authorities  for  the  construc- 
tion and  maintenance  of  roads.  Advances  may  be  made  by 
loan  or  grant  or  upon  such  terms  and  subject  to  such  conditions 
as  the  Board  may  impose. 

SWITZERLAND.  The  highways  in  Switzerland  come  under 
the  direct  supervision  of  the  authorities  of  the  separate  Cantons. 
The  State  exercises  no  control  over  the  highways  except  that 
by  reason  of  the  fact  that  it  assists  the  Cantons  financially  to 
some  extent,  it  may  impose  certain  regulations  before  rendering 
such  assistance.  The  engineers  in  direct  charge  of  the  work 
must  be  technically  trained  men. 


30  ELEMENTS    OF   HIGHWAY   ENGINEERING 

OTHER  EUROPEAN  COUNTRIES.  In  Spain,  Italy,  Belgium, 
Austria,  and  Portugal  the  scheme  of  administration  of  highway 
construction  is  very  similar  in  each  case  to  that  of  France. 

UNITED  STATES.  In  the  United  States  there  is  no  national 
system  of  highways,  although  many  bills  proposing  national 
participation  of  the  government  in  the  construction  of  highways 
have  been  brought  before  Congress.  The  National  Highways 
Association,  after  a  thorough  investigation  of  foreign  systems 
and  the  several  interstate  trunk  highways  traversing  the 
United  States,  has  proposed  a  system  composed  of  fifty  thou- 
sand miles  of  national  highways. 

The  Office  of  Public  Roads  and  Rural  Engineering,  which 
is  a  branch  of  the  Department  of  Agriculture,  is  maintained  by 
the  Government  for  the  purpose  of  the  accumulation  and  dis- 
semination of  knowledge  with  reference  to  highways.  The  office 
is  equipped  with  laboratories  for  testing  certain  kinds  of  road 
materials.  It  also  supervises  the  construction  of  experimental 
roads  in  various  parts  of  the  country  with  a  view  to  showing 
the  different  localities  what  can  be  done  with  local  materials. 

States.  There  are  many  States  which  have  adopted  a  sys- 
tem of  highways  that  are  paid  for  either  wholly  or  in  part  by 
the  State.  Highway  work  undertaken  by  the  various  counties 
and  towns  within  the  States  is  usually  carried  out  without  any 
control  on  the  part  of  the  state  authorities  unless  financial  aid 
has  been  given  by  the  State.  The  administration  of  the  work 
in  the  various  States  is  usually  vested  in  a  commission,  a  com- 
missioner, or  a  state  engineer,  appointed  in  many  cases  by  the 
Governor  of  the  State,  subject  to  the  approval  of  the  state  legis- 
lature. Unfortunately,  politics  play  too  important  a  part  in 
these  appointments  and  seriously  interfere  with  the  establish- 
ment of  an  efficient  organization. 

New  Jersey  was  the  first  State  in  the  United  States  to  adopt 
a  policy  of  state  aid  for  the  construction  of  highways,  the  State 
Highway  Department  being  established  in  1891.  State  aid  is 
not  always  given  in  the  form  of  money.  There  are  several 
States  in  which  the  aid  consists  in  furnishing  engineering 
advice  and  assistance.  Only  a  brief  resume  of  highway  legisia- 


ADMINISTRATION  AND   LEGISLATION  31 

tion  as  enacted  by  a  few  States  will  be  given.  The  examples 
cited  are  typical  of  the  several  methods  of  administering,  finan- 
cing, and  developing  state,  county,  and  town  highways. 

Alabama.  The  State  Highway  Commission  consists  of  the 
Professor  of  Civil  Engineering  at  the  Alabama  Polytechnic  In- 
stitute, the  State  Geologist,  and  three  civilians  appointed  by 
the  Governor.  The  Commission  appoints  a  State  Highway  Engi- 
neer, whose  duties  are  to  prepare  road  maps  of  the  State  and 
to  give  engineering  advice  and  assistance.  The  annual  appro- 
priation minus  the  expenses  of  the  Commission  is  divided  equally 
among  the  different  counties  of  the  State.  Before  any  county  . 
can  obtain  its  allotment  it  must  appropriate  an  equal  sum. 

California.  The  Department  of  Engineering  consists  of  an 
advisory  board  composed  of  the  Governor,  who  acts  as  ex-ofncio 
Chairman,  the  State  Engineer,  the  General  Superintendent  of 
State  Hospitals,  the  Chairman  of  the  State  Board  of  Harbor 
Commissioners  of  San  Francisco,  and  three  members  appointed 
by  the  Governor.  A  highway  engineer  is  also  appointed  by  the 
Governor.  The  California  State  Highway  Commission  is  com- 
posed of  three  members  of  the  engineering  department,  appointed 
by  the  Governor.  The  highway  engineer  reports  to  the  Com- 
mission. An  $18,000,000  bond  issue  was  made  available  in 
1910  for  the  construction  of  a  system  of  state  highways.  The 
counties  are  required  to  pay  4  per  cent  interest  on  the  amount 
of  the  bond  issue  spent  within  the  county,  minus  a  sum  de- 
pending upon  the  relation  between  the  bonds  matured  and  the 
bonds  outstanding.  The  state  highways  are  maintained  with 
the  funds  derived  from  license  fees  on  motor-vehicles.  Several 
roads  in  districts  which  are  too  poor  to  pay  for  them  are  con- 
structed and  maintained  by  state  appropriations. 

Connecticut.  A  State  Highway  Commissioner,  who  is  re- 
quired to  be  a  capable  highway  builder,  is  appointed  by  the 
Governor  with  the  approval  of  the  senate.  The  highway  com- 
missioner has  complete  authority  with  reference  to  the  con- 
struction and  maintenance  of  trunk-line  state-aid  roads.  The 
trunk  highways  laid  out  in  1913  are  constructed  and  maintained 
at  the  expense  of  the  State.  State  aid  may  be  obtained  by  any 


32  ELEMENTS   OF   HIGHWAY  ENGINEERING 

town  upon  written  application  of  the  selectmen  of  that  town. 
Towns  which  have  a  valuation  of  over  $1,250,000  are  entitled 
to  receive  from  the  State  three-fourths  of  the  cost  of  construc- 
tion of  roads,  under  provision  of  the  state-aid  act,  and  towns 
under  $1,250,000  valuation  receive  seven-eighths  of  the  cost. 
The  amount  paid  by  the  State  for  the  construction  of  state-aid 
highways  is  limited  to  $500,000  per  year.  Money  for  the  con- 
struction of  trunk-line  and  state-aid  highways  is  obtained  from 
bond  issues.  Three-fourths  of  the  maintenance  of  state-aid  high- 
ways is  paid  by  the  State  and  one-fourth  by  the  towns.  All 
funds  received  from  license  fees  on  motor-vehicles  are  used  for 
the  maintenance  of  highways. 

Georgia.  State  participation  in  the  construction  of  highways 
is  under  the  supervision  of  the  State  Prison  Commission.  This 
Commission  is  authorized  to  purchase  road  machinery,  equip 
and  organize  male  felony  convicts  to  constitute  gangs  for  county 
highway  work.  The  convicts  are  apportioned  to  the  several 
counties  upon  the  basis  of  population. 

Illinois.  The  Highway  Commission  consists  of  three  persons, 
appointed  by  the  Governor,  who  serve  without  pay.  A  State 
Engineer  is  appointed  by  the  Commission.  The  Commission 
acts  in  an  advisory  capacity  and  may  be  consulted  by  any  of 
the  county,  city,  village,  or  township  highway  officials.  An  ap- 
propriation of  $100,000  per  year  is  made  for  the  support  of  the 
work  of  the  Commission,  which  work  includes  the  preparation 
of  road  and  bridge  plans,  estimates,  collection  of  statistics,  and 
experimental  work.  Annual  appropriations  are  made  for  the 
construction  of  state-aid  roads  and  bridges,  the  1914-1915  ap- 
propriation being  $700,000.  The  State  pays  one-half  the  con- 
struction of  roads  and  bridges  and  the  county  concerned  pays 
one-half.  The  cost  of  maintenance  of  the  state-aid  roads  and 
bridges  is  borne  by  the  State. 

Maryland.  From  1898  to  1904  engineering  advice  was  fur- 
nished to  the  various  road  officials  throughout  the  State  by  the 
Maryland  Geological  and  Economic  Survey,  which  received  an 
annual  appropriation  from  the  State  of  $10,000  for  this  purpose. 
In  1904  the  State  voted  to  appropriate  $200,000  annually  for 


ADMINISTRATION  AND   LEGISLATION  33 

state-aid  work,  the  money  to  be  spent  under  the.  direction  of 
the  Geological  and  Economic  Survey.  The  State  Roads  Com- 
mission, which  has  had  charge  of  the  highway  work  since  1910, 
consists  of  six  members  appointed  by  the  Governor.  The  work 
of  construction  and  maintenance  is  carried  out  by  an  engineer- 
ing organization  under  a  chief  engineer.  The  following  bond 
issues  have  been  approved  by  the  people:  1908,  $5,000,000; 
1910,  $1,000,000;  1912,  $3, 170,000;  1914,  $5,000,000.  The  funds 
from  these  bond  issues  are  used  for  the  construction  and  main- 
tenance of  trunk-line  highways.  State-aid  roads  are  also  con- 
structed in  the  various  counties,  the  cost  being  shared  equally 
by  the  county  and  the  State,  the  work  being  done  under  state 
supervision.  The  maintenance  of  state-aid  roads,  however, 
is  carried  out  by  the  county  authorities  with  state  super- 
vision. The  funds  for  state-aid  roads  are  provided  by  direct 
appropriation. 

Massachusetts.  The  Massachusetts  Highway  Commission 
was  formed  in  1893  and  consists  of  three  members  appointed  by 
the  Governor.  A  chief  engineer,  appointed  by  the  Commission, 
is  in  charge  of  the  engineering  organization.  The  first  appro- 
priation for  the  construction  of  state  highways  was  made  in 
1894.  Many  bond  issues  have  been  voted  since  1894,  the  1915 
issue  being  at  the  rate  of  $1,000,000  per  year.  The  State  aids 
in  the  construction  and  maintenance  of  state  highways  and 
town  roads.  The  county  in  which  the  state  highway  is  located 
pays  25  per  cent  of  the  cost  of  construction.  A  sum  not  ex- 
ceeding 15  per  cent  of  the  amount  appropriated  by  the  State 
may  be  used  in  the  construction  of  town  roads  as  follows:  5  per 
cent  in  towns  having  a  valuation  of  less  than  $1,000,000,  the 
town  making  no  contribution;  5  per  cent  in  towns  having  a 
valuation  of  less  than  $1,000,000,  the  town  contributing  an  equal 
amount;  5  per  cent  in  towns  having  a  valuation  of  more  than 
$1,000,000,  the  town  contributing  a  like  amount.  No  state  aid 
can  be  given  until  a  petition  from  the  governing  body  of  the 
town,  county,  or  city  in  which  the  road  is  located  has  been 
received  and  approved  by  the  Commission.  Roads  declared 
state  highways  are  maintained  at  the  expense  of  the  State  and 


34  ELEMENTS   OF  HIGHWAY   ENGINEERING 

counties.  Town  roads  built  with  state  aid  are  maintained  by 
the  towns.  Funds  derived  from  fees,  fines,  etc.,  on  mo  tor- vehicles 
are  used  for  the  maintenance  of  highways  constructed  under 
the  supervision  of  the  Commission. 

New  Jersey.  The  State  Highway  Commission  consists  of 
the  Governor,  President  of  the  Senate,  Speaker  of  the  House  of 
the  Assembly,  State  Treasurer,  and  a  Commissioner  of  Public 
Roads  appointed  by  the  Governor.  Under  the  Commissioner  of 
Public  Roads  is  a  State  Supervisor  who  has  charge  of  the  engi- 
neering work.  The  State  participates  in  the  construction  and 
maintenance  of  state  highways  and  state-aid  county  highways. 
The  trunk-line  state  highways  are  constructed  and  maintained 
at  the  expense  of  the  State.  The  State  appropriates  $400,000 
annually  for  state-aid  road  construction,  40  per  cent  of  the  cost 
of  any  road  being  paid  for  by  the  State  and  60  per  cent  by  the 
county.  The  surveys  for  a  road  are  made  by  the  county  engi- 
neers at  the  expense  of  the  county.  Before  receiving  state  aid, 
the  plans  and  construction  have  to  be  approved  by  the  Com- 
missioner of  Public  Roads.  County  supervisors  and  county  en- 
gineers are  appointed  by  the  Boards  of  Freeholders  of  the  various 
counties. 

New  York.  The  State  Commission  of  Highways  of  New 
York  consists  of  the  Commissioner,  who  is  appointed  by  the 
Governor.  The  highways  are  divided  into  four  classes:  State 
and  county  highways,  county  roads,  and  town  highways.  The 
Commissioner  appoints  three  deputy  commissioners,  the  first 
deputy  having  charge  of  the  plans,  specifications,  and  execution 
of  all  contracts  pertaining  to  the  construction  of  state  and  county 
highways  and  county  roads;  the  second  deputy  having  charge 
of  the  maintenance  of  state  and  county  highways  and  county 
roads;  the  third  deputy  having  charge  of  the  repair,  improve- 
ment, and  maintenance  of  town  highways  and  bridges  and  county 
roads  and  bridges  in  the  Indian  reservation.  The  Commissioner 
also  appoints  nine  division  engineers,  who  have  charge  of  the 
construction  and  maintenance  of  the  state  and  county  highways 
in  their  respective  divisions  under  the  supervision  of  the  deputy 
having  jurisdiction  thereof.  County  superintendents  are  ap- 


ADMINISTRATION  AND   LEGISLATION  35 

pointed  by  the  boards  of  supervisors  of  the  various  counties, 
these  superintendents  being  subject  to  the  regulations  of  the 
Commissioner.  Town  superintendents,  who  are  elected  at  the 
town  meetings,  report  to  the  county  superintendents.  New  York 
ranks  first  in  the  amount  of  money  raised  for  the  construction 
of  highways  by  the  authorization  of  a  $50,000,000  bond  issue 
in  1906  and  by  the  passage  of  another  $50,000,000  bond 
issue  in  1912.  The  cost  of  improving  state  highways  is  borne 
entirely  by  the  State.  The  cost  of  improving  county  highways  is 
distributed  as  follows:  State,  50  per  cent;  county,  35  per  cent; 
town,  15  per  cent.  County  roads  are  improved  at  the  expense 
of  the  counties  but  the  State  contributes  50  per  cent  of  the 
amount  appropriated  by  counties  for  maintenance.  The  appro- 
priation made  as  state  aid  to  towns  for  the  construction  of  town 
highways  is  based  upon  the  amount  of  taxes  levied  per  mile  of 
highway  within  the  town.  No  town  under  this  scheme,  however, 
can  receive  an  amount  exceeding  $25  per  mile  for  the  total 
mileage  of  the  towns  outside  of  the  incorporated  villages.  The 
maintenance  of  the  state  and  county  highways  is  under  the 
control  of  the  Commission,  an  annual  appropriation  being  made 
to  cover  this  expense.  The  towns,  however,  are  required  to  pay 
$50  a  year  for  each  mile  of  state  and  county  highways  within 
their  borders  towards  the  expense  of  maintenance. 

Ohio.  A  State  Highway  Commissioner  is  appointed  by  the 
Governor.  The  Commissioner  appoints  three  deputy  commis- 
sioners, one  having  charge  of  a  bureau  of  construction,  one 
having  charge  of  a  bureau  of  maintenance  and  repair,  and  one 
having  charge  of  a  bureau  of  bridges.  The  Commissioner  and 
deputy  commissioners  must  be  civil  engineers  with  experience 
in  the  construction  and  maintenance  of  roads  and  bridges.  For 
construction  of  inter-county  highways  and  main-market  roads 
the  State  pays  50  per  cent,  the  county  25  per  cent,  the  town 
15  per  cent,  and  the  abutting  property-owners  10  per  cent. 
Funds  for  state  aid  are  raised  by  direct  appropriation  and  by 
an  annual  tax  levy  of  three-tenths  of  a  mill  on  all  taxable  property. 

Pennsylvania.  A  Highway  Commissioner  is  appointed  by 
the  Governor.  He  also  appoints  two  deputy  commissioners  and 


36  ELEMENTS   OF  HIGHWAY  ENGINEERING 

a  chief  engineer.  The  other  members  of  the  engineering  force 
are  appointed  by  the  Commissioner.  State  highways  are  built 
and  maintained  at  the  sole  expense  of  the  State.  State  aid  may 
be  obtained  by  a  county,  and  borough  or  township  applying 
jointly  or  separately.  In  the  first  case,  the  county  and  town- 
ship or  borough  pay  50  per  cent  and  the  State  50  per  cent  of  the 
cost  of  construction;  in  the  second  case,  50  per  cent  of  the 
cost  is  borne  by  the  State  and  50  per  cent  by  the  county,  borough, 
or  township  applying.  Funds  for  construction  and  maintenance 
are  provided  by  direct  appropriation. 

Rhode  Island.  A  State  Board  of  Public  Roads  composed  of 
five  civilians,  one  from  each  county  in  the  State,  was  appointed 
by  the  Governor  in  1902.  The  Board  appoints  an  engineer. 
Rhode  Island  was  the  first  State  to  establish  a  system  of  state 
trunk  highways.  Since  1902  several  direct  appropriations  for 
the  work  of  building  state  highways  have  been  made  by  the 
State  and  $1,800,000  in  bond  issues  have  been  authorized.  A 
state  highway  having  a  width  of  improved  surface  of  14  feet 
is  built  and  maintained  entirely  at  the  expense  of  the  State. 
Should  a  wider  road  be  desired,  the  town  through  which  the 
road  passes  pays  for  the  extra  width  over  14  feet.  The  whole 
width,  however,  is  maintained  by  the  State.  A  state-aid  law 
has  also  been  passed,  in  which  the  State  appropriates  a  sum 
equal  to  one-fifth  of  a  sum  raised  by  the  town.  The  sum  raised 
by  the  town  must  be  in  the  way  of  an  annual  appropriation 
and  must  be  equal  to  or  more  than  a  sum  of  20  cents  on  each 
$100  of  ratable  property  of  the  town.  The  town  is  also  re- 
quired to  vote  that  the  expenditure  of  this  money  shall  be  under 
the  direction  of  the  State  Board  and  for  the  maintenance  and 
repair  of  highways  and  bridges  other  than  state  highways. 
The  proceeds  from  motor-vehicle  fees  are  used  for  the  main- 
tenance of  state  highways. 

Municipalities.  The  administration  of  highways  within  the 
cities  is  usually  controlled  by  the  governing  body  of  the  city. 
"The  following  requisites  are  necessary  in  order  to  secure  satis- 
factory results  in  highway  administration:  (i)  Centralization 
of  authority  over  and  responsibility  for  all  work  relating  to 


ADMINISTRATION  AND   LEGISLATION  37 

highways  within  the  administrative  district;  (2)  such  flexibility 
of  organization  as  will  permit  a  concentration  of  force  on  any 
work  of  pressing  importance;  (3)  administrative  units  sufficiently 
large  to  permit  the  utilization  of  an  entire  force  and  equipment 
all  of  the  time,  reducing  overhead  charges  to  a  minimum  con- 
sistent with  efficiency  and  thoroughness;  (4)  get  rid  of  the 
prevalent  horror  of  a  bureaucracy.  If  such  a  bureaucracy  works 
well,  it  is  a  good  thing.  If  it  works  badly,  it  is  not  because  it 
is  a  bureaucracy,  but  because  it  is  not  well  organized;  (5)  direct 
and  undivided  responsibility  for  every  part  of  the  work,  each 
head  of  a  bureau  or  subdivision  to  be  made  to  realize,  however, 
that  his  own  particular  work  should  be  so  done  as  to  help  and 
not  to  hinder  that  of  other  bureaus  or  divisions;  (6)  promotion 
to  the  headship  of  bureaus  and  departments  to  be  made  from 
within  the  organization  when  possible,  not  necessarily  accord- 
ing to  seniority,  but  by  reason  of  peculiar  fitness.  When  it  is 
necessary  to  go  outside  of  the  organization  to  fill  such  a  place, 
the  appointee  should  be  one  who  has  already  made  good  in 
similar  work  in  some  other  place;  (7)  permanent  tenure  of 
office  for  those  in  responsible  charge,  so  that  continuity  of 
purpose  and  policy  may  be  assured."*  In  the  United  States 
the  carrying  out  of  the  work  is  accomplished  by  three  general 
methods  of  administration,  which  are  illustrated  by  a  brief  review 
of  the  practice  in  Boston,  Providence,  and  St.  Louis. 

Boston.  A  chart,  shown  in  Fig.  3,  illustrates  the  difference 
between  the  old  and  new  systems  of  administration  in  Boston. 
The  old  system  was  abandoned  in  favor  of  the  new  on  account 
of  the  lack  of  cooperation  between  the  departments  of  the 
City  Engineer,  the  Water  Commissioner,  and  the  Superinten- 
dent of  Streets.  These  departments  acted  independently  of 
one  another,  which  led  to  endless  confusion  and  waste  of  money. 
In  the  new  system  the  direct  controlling  officer  is  an  Engineer- 
Commissioner  of  Public  Works  who  reports  to  the  Mayor.  Under 


*  From  1913-1914  Lecture  by  Nelson  P.  Lewis,  Chief  Engineer,  Board  of 
Estimate  and  'Apportionment,  New  York  City,  in  the  Graduate  Course  in 
Highway  Engineering  at  Columbia  University. 


38 


ELEMENTS   OF   HIGHWAY  ENGINEERING 


this  Commissioner  are  three  deputy  commissioners,  one  having 
charge  of  the  sewer  and  water  division,  one  of  the  highway 
division,  and  one  of  the  bridges  and  ferries  division.  It  is  ap- 
parent that  in  this  last  arrangement  the  relations  of  the  three 


FIG.  3.     Old  and  New  Systems  of  Organization  of   Public  Works   Depart- 
ment, City  of  Boston. 

divisions  are  controlled  by  one  head,  who  can  insist  on  coopera- 
tion and  centralization  of  effort. 

Providence.  A  Commissioner  of  Public  Works,  appointed  by 
the  City  Government,  directly  controls  the  work  of  the  engi- 
neering department.  The  City  Engineer  heads  a  department, 
the  several  divisions  of  which,  such  as  bridges,  sewers,  streets, 
and  water-works,  are  in  charge  of  assistant  engineers.  The 
Commissioner  of  Public  Works,  who  is  not  an  engineer,  has  the 
final  decision  as  to  the  expenditure  of  money  appropriated. 
The  City  Engineer  reports  directly  to  the  Commissioner  as  to 
methods  of  construction,  which  recommendations  are  usually 
carried  out. 

St.  Louis.  In  this  city,  a  Commission,  composed  of  engineers, 
supervises  all  public  work.  Each  division  of  public  work  is 
under  the  control  of  a  member  of  the  Commission  and  has  its 
own  complete  organization.  The  work  of  all  the  divisions  is  co- 
ordinated by  the  Commission.  Since  the  different  members  of 
the  Commission  cooperate  with  each  other  in  their  various  lines 
of  work  through  the  medium  of  frequent  meetings,  the  result 
is  that  all  the  public  work  is  carried  out  with  a  minimum 


ORGANIZATION  39 

amount  of  delay  and  friction.    Important  meetings  of  the  Com- 
mission are  presided  over  by  the  Mayor. 

ORGANIZATION 

In  order  to  attain  efficiency  in  all  departments  of  work  to 
be  carried  out  under  the  jurisdiction  of  a  highway  department 
requires  that  the  duties  assigned  to  the  department  and  the 
personnel  and  interrelationship  of  the  several  units  of  the  or- 
ganization should  be  based  upon  the  following  fundamental 
principles:  (i)  a  highway  department  should  have  control  of 
all  departments  of  work  relating  to  the  substructure  and  super- 
structure of  highways  within  the  limits  of  the  right  of  way; 
(2)  all  positions  in  a  highway  department,  except  those  of  fore- 
men of  laborers  and  laborers,  should  be  occupied  by  men  with 
varying  degrees  of  engineering  training,  education,  and  experi- 
ence; (3)  the  personnel  and  the  work  of  the  organization  should 
not  be  affected  by  political  influence  or,  from  a  technical  stand- 
point, by  the  dictation  or  influence  of  a  layman  or  bodies  of 
laymen;  (4)  the  interrelationship  of  the  several  units  of  a  high- 
way department  should  be  based  upon  the  axiomatic  principles 
governing  the  organization  of  an  army,  in  that  there  should  be 
a  continuation  of  authority  from  the  most  minor  position  to 
the  administrative,  executive,  and  engineering  head  of  the  organi- 
zation; (5)  all  positions  in  a  highway  department  should  be 
filled  under  civil  service  regulations,  and  in  order  to  secure  the 
greatest  possible  , efficiency  and  competition  for  positions,  no 
residence  qualifications  should  apply  to  any  position. 

STATE  AND  COUNTY  DEPARTMENTS.  A  state  or  county 
highway  department  should  have:  (i)  control  of  the  con- 
struction and  maintenance  of  the  highways  within  its  borders 
which  come  under  its  jurisdiction;  (2)  charge  of  all  surveys, 
mapping,  and  design  connected  with  highways  and  bridges  con- 
structed or  maintained  by  the  department,  and  the  testing  of 
all  materials  used  on  the  work  of  the  department;  (3)  super- 
vision of  the  super-  and  substructures  of  electric  and  steam 
railroad  companies,  telegraph  companies,  telephone  companies, 


40  ELEMENTS  OF  HIGHWAY  ENGINEERING 

water-works  companies,  and  all  other  public  utilities  companies, 
in  so  far  as  the  control  and  maintenance  of  their  structures 
within  the  limits  of  highways  are  concerned;  (4)  power  to  formu- 
late the  traffic  regulations  covering  the  operation  of  motor-buses, 
motor-trucks,  other  types  of  motor-cars,  and  all  types  of  horse- 
drawn  vehicles  on  the  public  highways. 

Inspectors  and  all  engineers  having  charge  of  surveys,  map- 
ping, design,  construction,  and  maintenance  should  possess  a 
degree  of  engineering  training,  education,  and  experience,  de- 
pendent upon  the  responsibility  of  the  positions  which  they 
occupy.  As  an  example  of  necessary  requirements  for  the  higher 
positions  in  an  organization  will  be  cited  the  recommendations 
of  Prevost  Hubbard  and  the  author  while  serving  as  the 
Advisory  Board  on  Highways  to  the  Department  of  Efficiency 
and  Economy  of  the  State  of  New  York. 

The  Commissioner  of  Highways  shall  be  a  civil  engineer, 
who  has  had  responsible  charge  of  the  construction  and  main- 
tenance of  highways  for  at  least  five  years  and  who  is  a  full 
member  or  has  fulfilled  the  requirements  for  the  grade  of  full 
member  of  the  American  Society  of  Civil  Engineers  (a  M.  Am. 
Soc.  C.  E.  must  be  over  thirty  years  of  age,  have  been  in  active 
engineering  practice  for  ten  years,  and  have  had  responsible 
charge  of  work  for  at  least  five  years,  and  shall  be  qualified  to 
design  as  well  as  to  direct  engineering  works).  It  was  also 
recommended  that  under  the  Commissioner  of  Highways  there 
shall  be  three  deputy  engineers  and  twelve  division  engineers, 
each  of  whom  shall  be  a  civil  engineer  who  has  had  responsible 
charge  of  the  construction  and  maintenance  of  highways  for  at 
least  three  years  and  who  is  or  has  fulfilled  the  requirements 
for  the  grade  of  full  member  in  the  American  Society  of  Civil 
Engineers.  Each  of  the  deputies  shall  have  charge,  under  the  * 
direction  of  the  Commissioner  of  Highways,  of  all  work  in  four 
divisions.  The  division  engineers  shall  report  in  the  organization 
recommended  to  one  of  the  deputy  engineers.  In  each  division 
there  shall  be  engineers  in  charge  of  counties,  reporting  to  a 
division  engineer.  Each  division  engineer  shall,  in  his  division, 
and  each  county  engineer  shall,  in  his  county,  have  charge  of 


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ORGANIZATION  43 

the  construction  and  maintenance  of  all  state  and  ceunty  high- 
ways and  all  state  work  relating  to  town  highways  and  bridges. 
The  necessary  interrelationship  between  the  several  positions 
in  the  highway  department  of  a  state  or  county  is  shown 
in  Fig.  4. 

The  recommendations  were  based  upon  the  fundamental 
principle  that  those  responsible  for  the  expenditure  of  millions 
of  dollars  of  the  public  moneys  for  the  construction  and  main- 
tenance of  highways  must  have  such  experience  and  training 
as  a  highway  engineer  as  will  ensure  that  the  work,  for  which 
each  unit  of  the  organization  is  responsible,  shall  be  accom- 
plished economically  and  efficiently.  Also  the  recommendations 
were  based  on  the  belief  that  the  desiderata  stated  above  can 
be  best  accomplished  by  continuity  of  responsibility  for  a  given 
item  of  work  from  the  man  in  personal  charge  through  the 
county  engineer,  division  engineer,  and  deputy  engineer  to  the 
Commissioner  of  Highways. 

URBAN  DISTRICT  DEPARTMENTS.  The  fundamental  princi- 
ples underlying  a  highway  organization  for  a  municipality  are 
embodied  in  Fig.  5  *  and  amplified  in  the  following  explanatory 
statement.  "The  activities  coming  under  the  jurisdiction  of 
such  a  department  would  be:  The  design  of  all  work  pertaining 
to  the  highways,  including  parkways,  park  drives,  and  small 
highway  bridges;  all  engineering  work  relative  to  lines,  grades, 
inspection  of  construction,  etc.;  the  construction  and  main- 
tenance of  all  highways,  including  street  pavements,  country 
roads,  parkways,  park  drives,  etc.;  the  placing  of  subsurface 
structures  and  encroachments,  including  all  underground  con- 
duits, pipe  lines,  service  connections,  vaults,  steps,  street  signs, 
stands,  etc.;  permits  and  licenses  for  vehicles  of  all  kinds; 
street  cleaning  and  snow  removal;  collection  and  disposal  of 
ashes ;  collection  and  disposal  of  rubbish ;  collection  and  disposal 
of  garbage."* 

*  William  H.  Connell,  Chief,  Bureau  of  Highways  and  Street  Cleaning  of 
Philadelphia,  in  the  Journal  of  The  Franklin  Institute,  April,  1915. 


CHAPTER  III 
PRELIMINARY  INVESTIGATIONS 

A  reconnaissance  for  a  proposed  railway  includes  a  careful 
study  of  grades,  distances,  curvature,  cost  of  construction, 
earning  capacity  as  functions  of  location.  Preliminary  investi- 
gations in  railroad  engineering  have  always  been  necessary. 
Such  investigations  are  also  of  great  economic  importance  in 
highway  engineering.  Without  having  at  hand  the  data  secured 
by  preliminary  investigations,  it  is  usually  impracticable  for  a 
highway  engineer  to  design  satisfactory  and  economical  highways. 
FUNDAMENTAL  ELEMENTS.  A  preliminary  investigation  should 
cover  the  following  factors:  location,  foundation,  drainage, 
aesthetics,  width,  climatic  conditions,  traffic  census,  normal  and 
abnormal  speed  of  various  classes  of  traffic,  the  nature  of 
horses'  shoes  and  non-skidding  devices  used,  the  traffic  regu- 
lations in  force,  the  probable  change  in  the  character  and  amount 
of  traffic,  topographical  and  geological  structure  and  features, 
the  condition  and  character  of  cross-roads,  the  character  of 
existing  surface,  the  possible  diversion  of  traffic,  the  months 
available  for  construction,  local  highway  materials,  the  methods 
of  street  cleaning  and  maintenance  in  vogue,  and  the  character 
of  available  plant  equipment  and  labor. 

As  considerable  ambiguity  exists  in  regard  to  the  meaning 
of  the  terms  highway,  road,  street,  roadway,  pavement,  crust, 
and  wearing  course,  the  following  definitions*  are  given  in  order 
that  these  terms,  as  used  in  this  book,  may  be  understood. 

"Highway.  The  entire  right  of  way  devoted  to  public  travel, 
including  the  sidewalks  and  other  public  spaces,  if  such  exist." 

"Road.     A  highway  outside  of  an  urban  district." 

"Street.     A  highway  in  an  urban  district." 

"Roadway.  That  portion  of  a  highway  particularly  de- 
voted to  the  use  of  vehicles." 

*  1914  Proceedings,  American  Society  of  Civil  Engineers,  pages  3015  to  3019. 

44 


PRELIMINARY   INVESTIGATIONS  45 

"  Pavement.  The  wearing  course  of  the  roadway  or  foot- 
way, when  constructed  with  a  cement  or  bituminous  binder,  or 
composed  of  blocks  or  slabs,  together  with  any  cushion  or 
'binder'  course." 

"  Crust.  That  portion  of  a  macadam  or  similar  roadway 
above  the  foundation  consisting  of  the  road  metal  proper  with 
its  bonding  agent  or  binder." 

"Wearing  Course.  The  course  of  the  crust  or  pavement 
exposed  to  traffic." 

Location.  Grades,  curves,  distances,  cost  of  construction, 
and  serviceability  to  commercial,  industrial,  agricultural,  and 
social  interests  are  important  functions  of  location.  In  the  case 
of  roads  a  proper  consideration  of  the  above  factors  requires 
extended  investigations,  as  it  is  practicable  in  many  cases  to 
consider  several  locations,  materially  reduce  grades,  eliminate 
sharp  curves,  and  even  select  new  layouts  without  entailing 
excessive  property  damages.  Streets  are  more  definitely  located 
than  roads.  However,  grades  should  receive  careful  considera- 
tion, as  the  advantages  resulting  from  grade  reductions  are  in 
some  cases  worth  many  times  the  property  damages  incurred. 

Foundations.  The  foundation  on  which  the  roadway  is  to 
rest  is  of  utmost  importance,  and  hence  should  receive  more 
than  a  superficial  examination.  The  failure  of  many  highways 
has  been  caused  by  poor  foundations  or  improper  drainage. 
Experience  will  have  shown  what  may  be  expected  under  cer- 
tain conditions  in  localities  where  highways  have  been  built 
for  a  number  of  years.  In  new  country  where  no  improved 
highways  exist,  test  pits  may  be  dug  at  frequent  intervals  along 
the  proposed  location  and  the  material  encountered  examined. 
Under  certain  conditions  an  old  earth  road-bed  may  present  a 
very  fair  appearance  at  the  time  it  is  observed,  but  there  may 
be  other  times  of  the  year  when  this  same  piece  of  road  would 
be  nothing  more  than  a  veritable  mud-hole,  seemingly  without 
bottom.  A  change  of  line  to  avoid  bad  foundations  may  be 
very  apparent.  Much  can  be  learned  by  careful  inquiries. 

Drainage.  Drainage  is  so  closely  allied  to  foundations  that 
it  is  rather  difficult  to  discuss  one  without  considering  the  other. 


46 


ELEMENTS    OF  HIGHWAY  ENGINEERING 


Those  places  where  the  foundations  can  be  improved  by  sub- 
drainage  should  be  determined.  There  will  probably  be  numer- 
ous instances  where  water  at  the  sides  of  the  highway  will 
indicate  the  presence  of  ground  water  in  the  vicinity  which 
might  easily  be  removed  by  proper  drainage.  Much  may  be 
learned  with  regard  to  the  surface  drainage  also.  The  engineer 


FIG.  6.     Clay  at  Foot  of  Side  Hill.     Road  Covered  with  Snow  when  Survey 

was  Made. 


in  making  his  investigation  may  not  be  on  the  highway  at  a  time 
to  note  the  worst  conditions.  (See  Fig,  6.)  For  instance,  water 
may  flow  over  the  street  or  road  at  certain  points  in  great  storms ; 
there  may  have  been  occasions  when  the  middle  of  the  highway 
has  been  gullied  out  by  the  water  to  a  great  depth;  some  places 
that  appear  to  be  useless  waterways  may  flow  full  at  certain 
seasons  of  the  year.  Information  relative  to  the  above  points 
is  extremely  helpful  in  making  an  intelligent  design. 

Width.  There  are  many  cases  where  the  property  has  en- 
croached on  the  lines  of  the  highway  to  such  an  extent  that  if 
the  lines  are  adhered  to  only  a  very  narrow  carriageway  could 
be  built.  In  some  places,  where  the  above  conditions  are  ap- 
parent, a  study  of  the  deeds  and  old  maps  in  the  recorder's 
office  will  be  sufficient  to  determine  the  correct  lines.  The 


PRELIMINARY   INVESTIGATIONS  47 

nature  of  probable  future  traffic  will  largely  determine  the  neces- 
sary width  of  the  carriageway.  A  study  of  the  development  of 
places  in  the  near  vicinity,  of  their  relationship  with  one  another, 
and  of  their  industries  will  help  solve  the  problem.  Had  some 
engineers  been  far-sighted  enough,  the  narrow  streets  encoun- 
tered in  our  principal  cities  would  never  have  been  built  and 
the  costly  improvements  which  are  being  undertaken  at  the 
present  time  to  overcome  these  "mistakes"  would  never  have 
been  necessary. 

Local  Materials.  It  has  been  said  that  the  ideal  engineer 
is  the  one  who  will  find  one  dollar  sufficient  where  the  ordinary 
man  would  spend  two.  There  is  no  better  opportunity  to  put 
this  into  practice  than  in  highway  engineering.  A  thorough 
knowledge  of  the  materials  available  in  the  locality  may  sug- 
gest some  method  of  construction  to  be  adopted  that  otherwise 
would  be  overlooked.  For  instance,  a  locality  may  be  devoid 
of  stone  and  the  cost  of  importing  stone  blocks  or  broken  stone 
may  be  excessive.  There  may  be  certain  industries  in  the  near 
vicinity  that  accumulate  a  lot  of  waste  material,  such  as  slag, 
for  example.  An  investigation  of  this  material  might  show  the 
practicability  of  its  use  in  construction.  The  nature  of  the 
soil,  the  location  of  gravel-pits,  sand-pits,  ledges,  and  quarries 
will  be  of  great  assistance  in  deciding  on  the  type  of  construction. 

Climatic  Conditions.  The  climatic  conditions  encountered 
have  to  be  borne  in  mind  in  selecting  the  type  of  road  or  pave- 
ment best  suited  for  any  particular  locality.  This  is  especially 
true  in  the  case  of  many  of  the  modern  bituminous  pavements. 
A  wide  range  of  temperature  will  necessitate  the  use  of  a  different 
bituminous  material  than  where  the  range  is  not  so  great.  The 
climatic  conditions  may  be  such  that  it  will  only  be  practical 
to  carry  on  the  construction  in  certain  months  of  the  year,  or 
it  may  be  possible  in  some  localities  to  do  work  throughout  the 
entire  year.  The  snowfall  may  be  so  great  and  the  weather  so 
cold  that  in  some  sections  the  highways  will  be  constantly 
covered  with  snow  during  the  entire  winter  season,  in  which 
case  the  cost  of  maintenance  may  be  materially  reduced. 

Maintenance.     If  a  road  is  to  be  efficiently  maintained  some 


48  ELEMENTS   OF   HIGHWAY  ENGINEERING 

saving  in  the  first  cost  might  be  made.  It  is  unwise,  however, 
to  suggest  a  cheaper  form  of  surfacing  with  the  expectation  of 
proper  maintenance,  unless  one  is  thoroughly  satisfied  that  the 
proper  degree  of  maintenance  can  be  obtained. 

Local  Environments.  The  nature  of  the  locality  through 
which  the  street  or  road  is  to  pass  should  be  ascertained.  For 
instance,  in  the  vicinity  of  hospitals  or  schools  it  is  desirable  to 
have  as  noiseless  and  sanitary  a  pavement  as  possible.  The 
same  quality  is  appreciated  in  residential  districts.  Near  docks, 
on  the  other  hand,  the  noise  feature,  although  objectionable,  is 
not  of  so  much  consequence.  The  grade  of  the  highway  will 
also  influence  the  selection  of  the  type  of  surface.  On  steep 
grades  taking  heavily  laden  vehicles  drawn  by  horses  a  surface 
must  be  furnished  which  will  provide  a  firm  foothold,  and  at 
the  same  time  withstand  the  wear. 

Esthetics.  In  highway  designing  aesthetics  is  sadly  neg- 
lected in  this  country.  We  do  little  to  beautify  our  highways, 
whereas  in  some  of  the  European  countries  the  sides  of  the 
highway  are  bordered  with  beautiful  trees  and  parkings,  which 
not  only  improve  the  appearance  of  the  highway,  but  also  make 
it  more  comfortable  for  use.  It  should  be  remembered  that 
trees  are  a  valuable  asset,  and  in  reconstructing  a  highway 
extreme  care  should  be  taken  not  to  destroy  them.  There  are 
places  where  a  slight  change  of  line,  grade,  or  width  would 
preserve  trees  that  otherwise  might  have  to  be  removed.  The 
purpose  for  which  a  highway  is  to  be  used  should  be  taken  into 
consideration.  For  instance,  in  the  case  of  a  proposed  park 
system,  an  investigation  might  disclose  some  very  beautiful 
natural  surroundings  through  which  the  road  should  pass.  The 
alignment  of  the  highway  in  this  case  should  be  studied  with 
the  idea  of  changing  the  natural  conditions  as  little  as  possible. 

The  appearance  of  the  finished  highway  and  its  relation  to 
the  environments  should  always  be  kept  in  mind.  Notes  should 
be  taken  regarding  the  abutting  property  and  the  approaches 
to  the  property  from  the  highway.  The  frontages  of  many 
fine  country  estates  along  highways  have  been  marred  because 
no  attention  has  been  paid  to  this  detail.  Within  the  cities 


PRELIMINARY   INVESTIGATIONS 


49 


the  investigation  should  be  made  particularly  thorough  with 
reference  to  street  intersections.  Poorly  designed  street  inter- 
sections are  an  ever  present  eyesore. 

Traffic  and  Its  Classification.  One  of  the  most  important 
considerations  in  a  preliminary  investigation  is  that  of  traffic. 
The  inherent  value  of  statistics  relative  to  traffic  on  all  classes 


FIG.  7,     Heavy  Load  of  Stone  on  3-inch  Tires. 


of  highways,  obtained  previous  to  construction,  is  recognized 
by  engineers  who  are  familiar  with  the  problems  of  modern 
highway  engineering,  and  who  take  into  careful  consideration 
the  economics  of  construction  and  maintenance. 

Various  classifications  of  the  traffic  to  which  the  highways 
are  subjected  have  been  proposed  from  time  to  time.  All 
classifications  have  been  dependent  primarily  upon  the  different 
effects  of  various  types  of  traffic  upon  the  several  kinds  of 
roads  and  pavements.  Before  considering  the  various  groupings 
of  traffic  employed  and  the  nature  of  the  information  to  be 
ascertained  through  the  medium  of  a  traffic  census,  the  gener- 
ally recognized  effects  on  roadways  of  horse-drawn  vehicles, 
touring-cars,  motor  trucks,  motor-buses  and  traction-engines 
will  be  briefly  stated. 


50  ELEMENTS   OF   HIGHWAY  ENGINEERING 

Effect  of  Horse-Drawn  Vehicles.  The  water-bound  broken 
stone  road,  if  built  with  the  proper  materials  and  properly 
maintained,  will  successfully  withstand  the  conditions  imposed 
by  this  class  of  traffic  up  to  a  tonnage  life  of  100,000  tons  per 
yard  of  width.  In  cases  where  very  heavy  loads  on  narrow  tires 


FIG.  8.     Ruts  Caused  by  "Tracking." 

(see  Fig.  7)  have  been  drawn  over  surfaces  in  a  soft  condition 
the  surface  has  been  cut  through  and  totally  destroyed.  The 
so-called  " horse  path'7  frequently  seen  on  country  highways  is 
formed  in  the  center  of  the  road  by  the  horses'  feet  due  to  con- 
stant tracking.  This  condition  is  also  due  to  the  use  of  a  soft 
stone  which  makes  the  surface  readily  susceptible  during  a  dry 
season  to  the  disintegrating  blows  of  the  horses'  hoofs.  The 
effect  of  "  tracking  "  is  shown  in  Figs.  8  and  9. 

In  connection  with  certain  types  of  surfaces  constructed  with 
bituminous  materials  the  horse-drawn  traffic  has  been  noticed 
to  be  very  destructive.  For  instance,  where  the  application  of 
a  coat  of  heavy  asphaltic  oil  and  stone  chips  or  gravel  has  been 
adopted  as  a  method  of  maintaining  the  broken  stone  roads, 
it  has  been  proved  in  several  instances  that  it  is  a  failure  where 
it  is  subjected  to  a  large  amount  of  heavily  loaded  horse-drawn 
vehicles.  When  the  traffic  is  composed  largely  of  horse-drawn 


PRELIMINARY   INVESTIGATIONS 


51 


vehicles,  a  seal  coat  of  bituminous  material  has  been  found 
necessary  to  preserve  the  surface  of  certain  bituminous  pave- 
ments constructed  either  by  the  penetration  or  mixing  method, 
as  the  blows  of  the  horses'  feet  would  otherwise  dislodge  the 
individual  stones  of  the  mosaic  surface. 

Effect  of  Touring-Cars.  The  theory  that  the  destructive 
force  of  the  motor-car  travelling  at  high  speeds  is  due  to  the 
suction  developed  underneath  the  tires  has  never  been  sub- 
stantiated. That  there  is  some  suction  at  this  point  cannot  be 
disputed.  The  main  destructive  effect,  however,  is  produced 
by  the  driving  wheels.  This  fact  was  clearly  proved  by  experi- 
ments, made  by  the  United  States  Office  of  Public  Roads,  with 
an  automobile  of  the  touring-car  type  which  was  driven  along 
a  road  at  varying  speeds  of  from  fifteen  to  seventy  miles  per 
hour.  Dust  raised  by  the  front  wheels  was  of  a  small  and 


FIG.  9.     Wear  of  Stone  Blocks  Caused  by  "Tracking." 

practically  uniform  amount  regardless  of  the  speed  of  the  car, 
while  the  dust  underneath  the  back  wheels  increased  in  a  marked 
degree  with  the  speed. 

The  destructive  agent  is  a  shearing  force  developed  between 
the  wheel  and  the  road.  This  force  is  ever  present  while  the 
car  is  in  motion  and  increases  with  the  speed  and  weight.  It 


52  ELEMENTS    OF   HIGHWAY  ENGINEERING 

is  also  known  that  there  is  more  or  less  slip  to  the  driving  wheels. 
It  has  been  found  that  in  travelling  a  certain  distance,  the  rear 
wheels  revolve  more  times  than  the  front,  due  to  the  fact  that 
when  the  wheels  leave  the  ground  in  passing  over  uneven  places 
the  engine  races.  The  successive  waves  across  the  surface  of 
many  water-bound  broken  stone  roads  which  are  subjected  to 
a  heavy  motor-vehicle  traffic  are  without  doubt  produced  by 
this  constant  pounding  action.  As  long  as  the  motor-cars  travel 
in  a  straight  line  there  is  very  little  side  slip  unless  the  road  is 
in  a  slippery  condition.  On  curves,  however,  there  is  a  terrific 
slew  of  the  rear  wheels,  which  is  very  destructive  if  the  car  is 
travelling  at  a  high  speed. 

Effect  of  Motor  Trucks.  The  motor  truck  is  being  rapidly 
adopted  by  many  interests  in  the  United  States.  (See  Fig. 
10.)  During  1914  in  the  State  of  New  York  there  were 
over  15,300  motor  trucks  in  operation.  This  kind  of  traffic 
is  presenting  a  very  serious  problem  which  must  be  met  in 
the  construction  of  highways.  The  trucks  are  equipped  with 
either  a  solid  smooth  tire  or  a  pneumatic  tire,  a  twin  tire  fitted 
with  rubber  blocks  or  a  metal  tire.  The  weights  carried  vary 
from  500  pounds  to  about  15  tons,  making  the  total  weight  in 
the  neighborhood  of  20  tons  for  the  heaviest  trucks,  approxi- 
mately two-thirds  of  which  is  carried  by  the  rear  axle.  The 
heaviest  cars  are  built  to  carry  their  loads  at  a  speed  of  about 
fifteen  miles  per  hour.  It  is  apparent  that  this  class  of  traffic 
presents  conditions  which  ordinary  roadways  have  not  been 
built  to  withstand.  In  order  successfully  to  combat  the  effect 
of  these  heavy  loads,  more  attention  must  be  paid  to  the  con- 
struction of  the  foundations  to  support  the  loads,  while  the 
surface  must  be  constructed  to  withstand  the  grinding  action 
of  the  wheels. 

Motor  trucks,  as  an  integral  part  of  a  census  classification, 
are  also  an  important  factor  on  account  of  the  relationship  of 
their  dimensions  to  the  required  width  of  roadways.  According 
to  A.  F.  Masury,*  for  trucks  of  from  i  to  10  tons  capacity, 

*  Chief  Engineer,  International  Motor  Company,  New  York  City. 


Courtesy  of  the  International  Motor  Company. 

FIG.  10.     Commercial  Motor  Trucks  Hauling  Lumber. 


Courtesy  of  the  International  Motor  Company. 

FIG.  II.     Closed  Motor-Bus. 


54 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


the  extreme  width  varies  from  68  to  93  inches  and  the  wheel 
base  from  12  to  i6y£  feet. 

Effect  of  Motor-Buses.  The  development  of  motor-bus  traffic 
in  England,  France,  and  Germany  has  been  rapid  since  1905. 
In  the  United  States  motor-bus  traffic  had  not  become  an  im- 
portant factor  on  highways  outside  of  urban  districts  prior  to 


Courtesy  of  the  International  Motor  Company. 

FIG.  12.     Open  Motor-Bus. 


1912.  The  rapid  development  of  motor-bus  routes  on  state  and 
county  highways  is  well  illustrated  by  the  status  of  this  type 
of  traffic  in  the  State  of  New  York  in  1914.  On  the  125  motor- 
bus  routes  in  operation,  the  motor-buses  carried  from  5  to  40  pas- 
sengers, had  a  rating  of  horse-power  from  20  to  75,  and  weighed 
loaded  from  i>^  to  8  tons.  (See  Figs,  n  and  12.)  The  effect  of 
motor-buses  on  roadway  surfaces  is  similar  to  that  produced  by 
motor  trucks  of  equal  weight  travelling  at  the  same  speed. 

Effect  of  Traction- Engines.      In   1896  a  committee  of  the 


PRELIMINARY   INVESTIGATIONS 


55 


House  of  Commons  of  England  made  a  thorough,  investigation 
of  the  effect  of  traction-engines  on  roads  in  connection  with 
pending  regulations  governing  this  class  of  vehicles.  This  com- 
mittee concluded  from  the  evidence  which  it  gathered  that,  on 
a  highway  where  either  the  foundation  was  bad  or  the  stone 
was  of  a  poor  grade,  this  kind  of  traffic  caused  excessive  damage, 
not  only  by  rutting  the  road,  but  also  by  destroying  the  shape 
to  such  an  extent  as  to  require  complete  reconstruction. 

Traction-engine    traffic    in   the   United   States  has  caused 
serious  damage  to  earth,  gravel,  and  broken  stone  roads,  and 


FIG.  13.     Traction-Engine. 


many  types  of  bituminous  surfaces  and  bituminous  pavements  due 
to  the  destructive  action  of  the  metal  cleats  with  which  the  rear 
wheels  of  many  traction-engines  are  equipped.  (See  Fig.  13.) 

Loads  and  Tire  Widths.  As  early  as  1823  regulations  gov- 
erning the  allowable  loads  and  widths  of  tires  for  horse-drawn 
vehicles  were  included  in  the  General  Turnpike  Act  of  England. 

The  following  regulations  relative  to  traction-engines  were 
prescribed  in  England  in  1896:  the  maximum  weight  of  a  loaded 
trailer  to  be  8  tons,  the  minimum  width  of  tires  in  this  case 
to  be  8  inches,  with  an  amendment  to  the  effect  that  a  single 


56  ELEMENTS   OF  HIGHWAY  ENGINEERING 

trailer  might  carry  a  single  piece  weighing  over  16  tons,  pro- 
vided the  width  of  tires  is  not  less  than  8  inches.  Traction- 
engines  drawing  trailers  must  have  tires  which  are  2  inches  wide 
for  each  ton  of  weight  of  the  traction-engine,  unless  the  diameter 
of  the  wheel  be  over  5  feet,  in  which  case  the  width  of  tire  may 
be  reduced  in  such  proportions  as  the  diameter  is  increased. 
The  tires  of  the  driving  wheels  may  be  shod  with  diagonal 
crossbars  or  with  wooden  blocks  of  certain  approved  design. 

The  1904  Motor  Car  Order  of  England  fixes  the  limit  of 
weight  of  a  loaded  motor-car  at  12  tons  and  a  loaded  trailer  at 
8  tons.  The  width  of  tire  depends  upon  the  size  of  the  wheel 
and  the  axle  load;  for  a  motor-car  the  minimum  width  was 
fixed  at  5  inches  and  for  a  trailer  at  3  inches.  These  regula- 
tions, however,  did  not  apply  to  tires  which  were  pneumatic 
or  made  of  a  soft  and  elastic  material.  A  distinction  w^as  also 
made  relative  to  the  speed  of  the  cars  depending  upon  the 
weight  and  the  kind  of  tires.  A  maximum  of  8  miles  per  hour 
was  provided  for  motor-cars  exceeding  3  tons  in  weight,  un- 
laden, or  with  a  registered  axle  weight  laden  exceeding  6  tons. 
The  speed  was  reduced  to  5  miles  per  hour  in  the  case  of  cars 
drawing  a  trailer.  The  speed  was  increased  to  12  miles  an 
hour  for  cars  equipped  with  pneumatic  or  other  elastic  tires, 
which  did  not  have  the  axle  weight  exceeding  6  tons,  and  was 
8  miles  per  hour  when  the  axle  weight  exceeded  6  tons. 

In  order  that  vehicles  should  not  damage  the  roadway,  the 
width  of  iron  tire  should  be  such  that  the  weight  per  inch  of 
tire  width  should  not  exceed  500  pounds  for  a  wheel  2  feet  in 
diameter,  with  an  allowed  increase  of  30  pounds  per  inch  for 
each  additional  3  inches  of  diameter. 

Some  of  the  heavy  loads  which  have  been  noted  on  the 
streets  of  New  York  City  are  as  follows:*  Cables  weighing  84 
tons  carried  equally  on  4  wheels,  the  truck  weight  adding  6 
tons;  girders  weighing  65  tons  carried  mainly  on  2  rear  wheels 
of  a  long  truck,  the  truck  weight  adding  2  tons  for  each  pair 
of  wheels;  an  automobile  truck  carrying  10  tons  on  4  wheels, 

*  By  Henry  B.  Seaman,  1912  Transactions,  American  Society  of  Civil 
Engineers,  pages  321-322. 


PRELIMINARY   INVESTIGATIONS 


57 


the  weight  of  the  truck  adding  6  tons;  a  coal  truck  hauled  by 
3  horses  carrying  7  tons,  the  truck  adding  2^  tons;  trucks 
which  carry  the  Lidgerwood  hoists  taking  a  load  of  15  tons,  the 
weight  of  the  truck  adding  3  tons;  the  standard  truck  for  gen- 
eral use,  hauled  by  2  horses,  carrying  a  load  of  5  tons  and 
weighing  2^/2  tons. 

Elements  of  Classification.    The  essential  elements  of  any 


Courtesy  of  the  Buffalo  Roller  Company. 

FIG.   14.     An  Example  of  Abnormal  Traffic,  Roller  Drawing  Loaded  Stone 

Wagons. 

classification  of  traffic  may  be  stated  as  follows :  (a)  differentia- 
tion between  horse-drawn  vehicle  traffic  and  motor-car  traffic; 
(b)  a  division  of  each  of  these  classes  of  traffic  into  pleasure 
and  commercial  traffic;  (c)  a  subdivision  of  commercial  traffic 
into  loaded  and  unloaded  vehicles;  (d)  the  determination  of 
the  weight  per  linear  inch  of  width  of  tire  of  all  types  of  com- 
mercial traffic,  a  factor  of  the  utmost  importance  in  the  design 
of  the  substructure  of  the  road;  (e)  a  subdivision  of  the  two 
classes  of  horse-drawn  vehicle  traffic  dependent  upon  the  number 


58  ELEMENTS    OF   HIGHWAY   ENGINEERING 

of  horses;  (/)  a  subdivision  of  pleasure  motor-car  traffic  upon 
the  basis  of  weight  and  speed,  since  in  many  instances  the 
greatest  damage  to  a  broken  stone  road  is  caused  by  seven-seat 
touring-cars,  limousines,  or  landaulets  travelling  at  speeds  of 
40  to  60  miles  per  hour;  (g)  a  subdivision  of  motor  truck  traffic 
upon  the  basis  of  weight  and  speed;  (ti)  provision  for  extraor- 
dinary character  of  local  traffic,  for  example,  traction-engines 
hauling  trailers  may  be  common,  see  Fig.  14,  while  in  other  cases 
motor-bus  traffic  may  be  regular  and  an  important  feature  or 
special  types  of  commercial  traffic  such  as  ice  wagons,  mill  drays, 
etc.,  may  use  the  highway. 

As  an  integral  part  of  the  requisite  investigation  preliminary 
to  economical  and  efficient  design,  other  facts  relative  to  traffic 
should  be  obtained,  as,  for  example,  the  direction  of  the  traffic, 
the  portion  of  the  roadway  occupied  by  various  kinds  of  traffic, 
the  kind  of  shoes  worn  by  the  horses  at  various  seasons  of  the 
year,  the  use  of  non-skidding  devices  employed  by  motorists, 
and  the  enforced  traffic  regulations  governing  the  use  of  the 
highway,  especially  with  reference  to  limitations  upon  speed 
and  loads  to  be  carried.  In  connection  with  the  preliminary 
investigations,  an  engineer  must  always  consider  the  change  in 
the  character  and  amount  of  traffic  that  is  liable  to  occur  after 
the  improvement  of  a  highway.  The  importance  of  an  estimate 
of  probable  traffic  cannot  be  overemphasized. 

Methods  Used  Prior  to  igoo.  French  engineers  have  for  a 
long  time  realized  the  importance  of  taking  a  traffic  census. 
A.  Moullee  states*  that  "Ten  censuses  of  traffic  over  the  entire 
country  have  been  undertaken  by  the  Department  of  Bridges 
and  Roads.  The  intervals  between  the  taking  of  these  com- 
prehensive data  have  varied  from  5  to  9  years.  The  first  census 
of  national  scope  was  taken  in  1844,  although  previous  to  that 
time  traffic  data  had  been  collected  in  certain  localities.  Traffic 
censuses  of  national  character  will  in  the  future  be  undertaken 
every  10  years.  Previous  to  the  advent  of  the  motor-car  the 
categories  of  traffic  noted  underwent  little  change.  Five  divi- 

*  See  "Highway  Engineering  as  Presented  at  the  Second  International 
Road  Congress,  1910,"  by  Blanchard  and  Drowne. 


PRELIMINARY   INVESTIGATIONS  59 

sions  were  recognized:  first,  freight  vehicles  and  those  for  agri- 
cultural purposes  when  loaded;  second,  public  vehicles  for 
common  transport  of  travellers  and  luggage;  third,  empty  freight 
or  agricultural  carts  and  private  carriages;  fourth,  unharnessed 
animals  of  large  size;  fifth,  light  live  stock." 

The  first  traffic  census  in  the  United  States  was  planned 
and  carried  out  under  the  direction  of  Capt.  F.  V.  Greene  in 
1885.  The  traffic  was  observed  on  six  consecutive  days  from 
7  A.M.  to  7  P.M.  Night  traffic  was  not  counted,  and  no  allow- 
ance was  made  for  the  same.  The  classification  adopted  was 
as  follows: 

One-horse  carriages,  empty  or  loaded 

One-horse  wagons,  empty  or  light  loaded      [•    less  than  I  ton 

One-horse  carts,  empty 

One-horse  wagons,  heavy  loaded 

One-horse  carts,  loaded  [•    between  i  and  3  tons 

Two-horse  wagons,  empty  or  light  loaded 

Wagons  and  trucks  drawn  by  2  or 

more  horses,  heavy  loaded  }    over  3  tons 

There  were  several  censi  made  in  the  United  States  and 
Canada  based  on  this  method.  It  is  self-evident  that  the  above 
classification  is  not  complete  enough  to  cover  modern  conditions. 

Methods  Used  Since  igoo.  Since  the  advent  of  the  motor- 
car, traffic  classifications  have  undergone  a  transformation.  The 
most  comprehensive  is  that  proposed  by  the  Road  Board  of 
England.  The  classification  includes  the  following  list  of 
vehicles : 

Tramcars  (Electric,  Steam,  or  Horse). 
Motor  Vehicles: 

Ordinary  Motor-cars  (including  cabs). 

Motor  Omnibuses. 

Motor  Delivery  Vans. 

Heavy  Motor  Lorries. 

Tractors  or  Traction-Engines  (Trailers  are  to  be  counted  as  additional 
vehicles,  i.e.,  a  traction-engine  with  two  trailers  would  be  entered  as  3). 

Motor  Bicycles  and  Tricycles. 

Any  other  Motor  Vehicles  not  included  under  any  of  the  above  heads. 
Horse- Drawn  Vehicles: 

Omnibus  (including  Public  Service  and  Hotel). 

Two-wheeled  Vehicles  (cne  horse). 

Two-wheeled  Vehicles  (two  horses,  or  more). 

Four-wheeled  Vehicles  (one  horse). 

Four-wheeled  Vehicles  (two  horses,  or  more). 


60 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


Other  Traffic: 

Ordinary  Bicycles  and  Tricycles. 

Herds  of  Cattle  (if  more  than  five  in  number)  to  be  entered  as  one. 

Flock  of  Sheep  and  Pigs  (if  more  than  five  in  number)  to  be  entered  as  one. 

Horses  (led  or  ridden). 

The  following  classification  recommended  by  the  Special 
Committee  of  the  American  Society  of  Civil  Engineers  on 
"Materials  for  Road  Construction"  is  typical  of  American 
practice. 


Comir 

icrcial 

Passenger 

Empty 

Loaded 

Pleasure 

One-horse  vehicles  

Two  or  three-horse  vehicles  

Four  or  more  horse  vehicles  

Motor  cycles 

runabouts 

touring  cars  (open  or  closed) 

buses  

"       trucks.. 

Methods  of  Taking  Traffic  Censi.  After  the  classification 
of  the  traffic  has  been  adopted,  the  methods  of  securing  traffic 
data  must  be  considered.  The  method  selected  will  be  influ- 
enced by  the  amount  of  time  at  the  disposal  of  the  engineer 
and  the  character,  amount,  and  distribution  of  the  traffic  to 
which  the  highway  in  question  is  subjected.  In  case  the  loca- 
tion of  the  highway  to  be  built  in  a  given  period  is  known  over 
a  year  in  advance  of  construction,  a  comprehensive  plan  cover- 
ing observations  throughout  the  year  should  be  adopted  in  order 
to  secure  complete  information.  In  many  instances,  however, 
perhaps  only  a  month  will  be  available  in  which  to  make  inves- 
tigations preliminary  to  design.  In  either  case,  it  is  essential 
that  as  complete  information  as  possible  should  be  secured 


PRELIMINARY   INVESTIGATIONS  61 

relative  to  the  nature  of  the  traffic  on  any  given  highway  before 
a  plan  is  adopted. 

As  the  primary  object  of  any  traffic  census  is  to  secure 
data  covering  both  normal  and  abnormal  traffic  of  all  classes, 
it  is  essential  to  incorporate  in  a  plan  definite  provision  for 
securing  the  above  information  rather  than  to  depend  upon  a 
haphazard  selection  of  days  to  furnish  the  facts.  As  an  illus- 
tration of  varying  local  conditions  may  be  cited:  exceptional 
horse-drawn  vehicle  traffic,  consisting  of  produce  wagons,  be- 
tween the  hours  of  midnight  and  6  A.M.  during  certain  seasons 
of  the  year;  market  days,  fair  days,  and  other  special  events 
in  connection  with  which  both  pleasure  and  commercial  traffic 
may  be  excessive;  periodical  heavy  shipments  by  special  indus- 
tries using  the  highway  in  hauling  raw  material  or  in  shipping 
the  manufactured  article;  through  traffic  at  certain  periods  of 
the  day,  week,  or  year  as,  for  example,  motor-car  traffic  be- 
tween residential  communities  or  summer  colonies  and  cities. 
In  many  cases  it  is  essential  to  obtain  the  following:  normal 
winter  traffic,  normal  summer  traffic,  and  abnormal  summer 
motor-car  traffic.  It  should  be  borne  in  mind  that  from  the 
standpoint  of  the  proper  design  of  the  highway,  it  is  necessary 
to  know  approximately  the  total  yearly  traffic,  which  is  a  func- 
tion of  both  the  normal  and  abnormal  traffic,  and  also  the 
amount  of  abnormal  traffic  of  various  types  at  different  periods 
of  the  year. 

Three  comprehensive  plans  for  taking  traffic  census  through- 
out the  year  have  been  used:  First,  to  take  the  traffic  in  periods 
of  6  or  7  consecutive  days;  second,  to  distribute  the  recording 
days  throughout  a  given  season  by  starting  on  a  given  day  of 
the  week,  for  example,  a  Monday,  then  take  the  traffic  on 
the  Tuesday  of  the  following  week  or  at  an  interval  of  15  days, 
and  so  on  during  the  season;  third,  for  the  season  from  April 
to  October  inclusive  the  traffic  could  be  taken  during  four 
periods  of  3  days  each;  one  period  being  in  April,  May,  or 
June,  one  in  July,  one  in  August,  and  one  in  September  or 
October.  As  local  conditions  may  dictate,  either  Friday,  Satur- 
day, and  Sunday  or  Saturday,  Sunday,  and  Monday  could  be 


62  ELEMENTS   OF  HIGHWAY   ENGINEERING 

taken,  thus  ensuring  information  relative  to  the  usual  abnormal 
Sunday  motor-car  traffic,  while  the  Friday  or  Monday 
traffic  would  give  a  fair  indication  of  the  normal  week-day 
traffic.  In  the  months  from  November  to  March  inclusive, 
two  3-day  periods  would  be  taken  in  certain  cases;  one  in 
November  or  December,  the  other  in  February  or  March.  This 
distribution  of  the  periods  would  furnish  statistics  of  the  normal 
traffic  in  this  season,  and  would  also  afford  opportunity  for  a 
study  of  traffic  detail  and  the  condition  of  the  highway  during 
the  winter  season. 

The  number  of  consecutive  hours  which  should  be  taken 
during  the  day  will  depend  upon  local  conditions  and  the  period 
of  the  year  when  observations  are  made.  In  many  cases,  espe- 
cially in  municipalities,  24  hours  will  be  absolutely  necessary, 
while  in  certain  cases  8  or  15  hours  will  be  satisfactory.  It 
must  be  borne  in  mind  that  the  facts  ascertained  are  used  as  a 
basis  for  an  estimate  of  traffic  and  hence  minute  detail  should 
not  be  obtained  at  unwarranted  expense. 

What  has  previously  been  said .  in  regard  to  taking  traffic 
outside  of  cities  applies  to  a  method  that  may  be  adopted  for 
this  purpose  within  the  cities.  The  method  to  be  adopted  in 
any  case,  however,  will  vary,  depending  upon  local  conditions. 
An  investigation  of  the  business  interests  situated  on  the  street, 
the  merchandise  which  is  handled,  and  the  general  routes  taken 
by  traffic  from  the  railroad  centers  or  docks  must  be  made 
before  it  is  possible  to  decide  on  an  intelligent  plan  for  taking 
the  census.  In  residential  districts  the  problem  is  more  simple 
and  the  method  used  would  probably  be  very  similar  to  that 
proposed  for  highways  outside  of  built-up  districts. 

Traffic  Regulations.  The  existing  traffic  regulations  and 
their  enforcement  should  be  carefully  looked  into,  as,  for  ex- 
ample, the  allowable  loads  and  the  prescribed  width  of  tires; 
whether  or  not  vehicles  or  tractors  with  extremely  wide  tires 
are  required  to  keep  to  one  side  of  the  center  of  the  road;  the 
speed  of  motor  vehicles,  etc. 

Diversion  of  Traffic.  The  construction  of  roads  and  streets 
often  necessitates  the  diversion  of  traffic  during  the  period  while 


PRELIMINARY   INVESTIGATIONS  63 

work  is  being  done.  In  the  business  districts,  it  is t possible  to 
close  off  one  or  two  blocks  or  to  build  half  the  width  at  a  time 
without  inconveniencing  the  public  to  any  great  extent.  On 
roads  it  is  not  such  an  easy  matter  to  provide  means  for  traffic 
to  pass  around  the  work,  and  if  it  cannot  be  accomplished  it 
may  preclude  the  use  of  some  method  that  would  otherwise 
be  used. 


CHAPTER  IV 
SURVEYING,  MAPPING  AND  DESIGN 

SURVEYS  FOR  ROADS 

GENERAL  SCOPE  OF  THE  WORK.  Methods  of  making  sur- 
veys for  highways  outside  of  urban  districts  vary  in  detail,  de- 
pending upon  the  proposed  location  of  the  highway.  If  the 
highway  is  to  be  located  upon  land  not  previously  used  for  such 
purposes,  the  survey  partakes  of  the  nature  of  a  railroad  recon- 
noissance.  If  the  highway  follows  approximately  the  lines  of  an 
existing  highway,  the  work  of  location  surveys  is  materially 
simplified. 

Before  a  survey  is  undertaken,  the  preliminary  location  should 
be  outlined  in  accordance  with  the  principles  mentioned  later 
under  Design.  With  this  information  at  hand,  the  chief  of  the 
survey  party  should  familiarize  himself  with  existing  maps  of 
the  locality  through  which  the  highway  will  pass.  The  United 
States  Geological  Survey,  in  conjunction  with  several  States,  has 
prepared  topographical  maps  that  give  the  contours  and  loca- 
tion of  highways.  In  many  States  local  maps  are  available 
which  give  topographic  details.  If  a  map  cannot  be  obtained 
and  the  highway  is  to  be  laid  out  in  a  new  location,  a  thorough 
reconnoissance  of  the  locality  should  first  be  made  as  in  rail- 
road work,  and  then  one  or  more  survey  lines,  the  number  de- 
pending upon  the  unevenness  of  the  country  and  right  of  way 
problems,  must  be  run  before  the  best  route  can  be  determined 
upon. 

Unfortunately,  surveys  for  this  class  of  highways  are  not 
usually  tied  in  with  any  system  of  points  previously  established 
by  triangulation  or  by  closed  traverses.  A  survey  on  one  road 
may  be  made  entirely  independent  of  that  on  another  road, 
since  the  roads  are  usually  so  widely  separated  that  there  is 

64 


SURVEYING,    MAPPING   AND   DESIGN  65 

no  important  relation  between  the  two.  Adjoining  surveys  on 
the  same  road  should  be  connected  with  each  other,  but  it  is 
not  essential  that  the  stationing  should  be  continuous.  A  map 
showing  the  plan  of  the  road  system  might  be  prepared  in  the 
course  of  time  by  combining  the  connected  surveys. 

A  complete  survey  includes  a  transit  line  and  topographic 
detail,  a  profile  and  cross-sections. 

THE  TRANSIT  LINE.  The  transit  line  may  or  may  not 
coincide  with  the  proposed  center  line  of  the  new  road. 

In  some  instances  the  transit  line  may  only  serve  as  a  refer- 
ence line  on  which  the  rest  of  the  location  is  based,  and  as  a 
working  line  from  which  the  proposed  work  can  be  staked  out. 
From  the  standpoint  of  convenience  this  method  has  several 
advantages.  The  traffic  conditions  may  be  such  that  the  work 
will  be  constantly  interrupted  unless  the  line  is  run  along  one 
side  of  the  highway,  rather  than  near  the  center.  In  some  cases 
where  a  car  track  is  located  in  the  road,  the  transit  line  may  be 
made  to  coincide  with  the  line  of  one  of  the  rails. 

The  surrounding  topographical  conditions  will  govern  the 
advisability  of  trying  to  obtain  a  field  location  of  a  center  line 
that  will  be  the  best  one  from  every  standpoint.  In  many  cases 
too  much  time  is  spent  in  the  field  to  accomplish  this  result. 
If  the  country  is  generally  flat,  and  if  proper  cross-section  levels 
are  taken,  it  will  be  possible  by  studying  the  plans  alone  to 
determine  upon  a  final  center  line  which  in  places  might  be 
several  feet  either  side  of  the  transit  line,  without  involving  any 
appreciable  error  in  the  stationing;  on  the  other  hand,  if  the 
country  is  rough,  a  change  of  line  from  the  transit  line  made 
in  the  office  will  probably  necessitate  another  survey. 

Stationing  and  Referencing.  The  transit  line  should  start 
from  an  initial  point  which  may  be  a  point  on  some  previous 
transit  line  or  some  assumed  point  carefully  tied  in  with  perma- 
nent objects.  The  line  is  made  up  of  tangents  and  curves. 
When  the  external  angle  between  the  tangents  is  less  than  10 
degrees,  the  stationing  may  be  measured  around  the  tangents 
without  appreciable  error,  although  a  curve  may  be  built  at  the 
intersection;  when  the  external  angle  between  the  tangents  is 


66  ELEMENTS   OF  HIGHWAY   ENGINEERING 

over  10  degrees,  it  will  be  necessary  to  figure  a  curve  in  order 
to  obtain  the  correct  stationing.  The  line  is  stationed  every  50 
or  100  feet,  depending  upon  the  character  of  the  topography 
and  the  accuracy  desired  for  the  estimate  of  grading.  Points 
established  on  the  line  are  liable  to  be  removed  or  covered  up 
during  the  construction,  hence  it  is  important  that  the  points 
at  the  intersections  of  the  tangents  should  be  carefully  tied  in 
to  objects  that  are  permanent  and  readily  accessible. 

Running  the  Line.  There  are  several  methods  of  running 
the  transit  line  and  of  locating  topography  with  reference  to  it. 
Only  one  method  will  be  described  which,  if  used,  will  give  re- 
sults within  the  limits  of  accuracy  necessary,  and  will  also  be 
found  expeditious.  First,  carefully  plan  out  the  location  of  the 
tangents  and  intersection  points.  The  transit  should  be  set  up 
at  the  intersections  of  the  tangents  from  which  points  the  tan- 
gents can  be  run  out  in  both  directions.  The  angle  between 
the  tangents  should  be  turned  off  at  least  twice  and  the  mean 
value  taken.  The  magnetic  bearings  of  the  tangents  should 
also  be  taken  as  a  check.  The  length  of  each  tangent  is  deter- 
mined with  the  steel  tape,  the  measurements  being  made  to 
the  nearest  hundredth  of  a  foot.  If  the  angle  at  the  intersection 
is  large  enough  to  warrant  the  use  of  a  curve,  the  stations  of 
the  point  of  curve  (P.  C.)  and  the  point  of  tangency  (P.  T.)  of 
the  proper  curve  are  figured  and  marked  on  the  line. 

Taking  Topography.  The  topography  includes  the  shape  of 
the  land  and  all  the  objects  such  as  houses,  walls,  fences,  gut- 
ters, curbs,  culverts,  bridges,  catch-basins,  trees,  monuments, 
edges  of  travelled  way,  poles,  ditches,  etc.,  in  fact,  any  object  that 
occurs  within  the  limits  of  the  survey  that  would  be  of  importance 
in  designing  the  road. 

All  topography  is  located  with  reference  to  the  tangents.  In 
locating  the  topography,  such  as  fences,  walls,  and  curbs,  it  is 
sufficient  to  record  the  stations  on  the  transit  line  opposite 
which  they  begin  and  end,  and  the  stations  at  intermediate 
points  which  will  define  their  alignment.  The  offsets  are  the 
perpendicular  distances  measured  from  these  stations  on  the 
transit  line  to  the  points  of  the  object  previously  noted.  The 


SURVEYING,   MAPPING  AND  DESIGN 


67 


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68  ELEMENTS   OF  HIGHWAY   ENGINEERING 

perpendicular  direction  will  be  determined  by  eye,  and  if  the 
object  is  not  at  too  great  a  distance  away  the  results  obtained 
are  sufficiently  accurate.  Offsets  and  plus  distances  for  loca- 
tion should  never  be  measured  closer  than  the  nearest  tenth, 
and  in  many  instances  where  the  topography  is  not  at  all  well 
defined  the  nearest  foot  will  be  sufficient.  When  the  P.  C.  is 
reached,  the  location  of  the  topography  should  be  made  from 
the  tangents.  The  distance  along  the  tangent  can  be  recorded 
as  a  plus  distance  from  the  P.  C.  to  the  intersection.  Starting 
again  at  the  intersection,  a  plus  distance  from  the  latter  can  be 
employed  until  the  P.  T.  is  reached  beyond  which  the  regular 
line  stationing  is  again  used. 

In  places  of  importance,  such  as  squares  and  villages,  where 
the  location  by  these  methods  might  be  somewhat  difficult,  the 
topography  can  be  readily  obtained  by  taking  angles  and  dis- 
tances to  the  various  points  or  by  means  of  the  stadia.  The 
last  method  will  often  be  found  very  convenient  in  locating 
objects  some  distance  away  from  the  transit  line.  A  sample 
page  of  transit  notes  is  shown  in  Fig.  15,  in  which  many  of 
the  points  above  mentioned  are  illustrated. 

LEVELS.  The  information  required  to  locate  all  topography 
includes  what  are  commonly  called  "cross-section  levels."  From 
the  information  thus  obtained  both  the  profile  of  the  transit  line 
and  the  shape  of  the  earth's  surface  at  known  intervals  along 
the  transit  line  can  be  plotted. 

Bench-Marks.  In  many  States  lines  of  levels  have  been  run 
starting  from  a  government  bench,  and  bench-marks  have  been 
established  on  these  lines  at  various  points  so  that  it  is  not  a 
difficult  matter  to  get  a  tide  water  datum  for  the  levels  on  any 
road.  If  this  has  not  been  done,  the  datum  may  be  assumed. 
Points  for  bench-marks  should  be  of  a  stable  and  permanent 
character,  and  their  location  should  be  clearly  described  so  that 
they  may  readily  be  found  at  any  time.  At  least  one  permanent 
bench-mark  should  be  established  every  1,000  feet  along  the 
survey. 

Running  the  Levels.  The  levels  may  be  taken  either  with 
a  transit  or  with  a  level.  The  transit,  if  in  adjustment  and 


SURVEYING,    MAPPING  AND   DESIGN  69 

carefully  used,  is  sufficiently  accurate  for  the  work,  but,  of 
course,  it  would  not  be  used  in  establishing  a  long  line  of  bench- 
levels.  When  the  rod  is  held  on  a  bench-mark  (B.  M.)  or  a 
turning  point  (T.  P.),  the  target  should  be  set  as  a  check  and 
the  rod  read  to  the  nearest  hundredth.  In  obtaining  the  eleva- 
tions of  the  earth's  surface,  it  is  not  necessary  to  use  the  target 
nor  to  read  the  rod  closer  than  the  nearest  tenth.  The  measure- 
ments of  the  plus  stations  and  offsets  to  points  at  which  levels 
are  taken  may  be  made  by  means  of  the  metallic  tape. 

Enough  points  should  be  taken  to  show  correctly  the  con- 
figuration of  the  earth's  surface.  This  may  be  accomplished 
by  taking  elevations  at  each  50-  or  loo-foot  station  along  the 
transit  line,  one  elevation  being  taken  on  the  transit. line  and 
sufficient  elevations  being  taken  on  a  line  perpendicular  to  the 
transit  line  at  these  stations  to  define  the  changes  in  slope  of 
the  earth's  surface.  The  elevations  of  car  tracks,  curbs,  gutters, 
edge  of  travelled  way,  bottoms  and  tops  of  banks,  together  with 
their  distances  out  from  the  transit  line,  should  be  taken  in  all 
cases.  Care  should  be  taken  to  extend  the  levels  out  far  enough 
on  both  sides  of  the  transit  line  sufficiently  to  cover  the  pro- 
posed construction.  Center  line  profiles  should  be  run  along 
every  intersecting  street  and  driveway  for  a  distance  of  at  least 
200  to  300  feet  from  the  transit  line.  Elevations  should  be 
taken  at  the  corners  of  houses,  at  the  ground  lines  and  at  the 
sills  where  there  is  any  possibility  of  the  improvement  disturbing 
the  property.  The  elevations  of  the  tops  and  bottoms  of  all 
culverts  and  drains  at  both  ends  should  be  determined.  In  the 
case  of  bridges,  elevations  should  be  taken  of  bridge  seats,  bridge 
floors,  tops  of  parapet  walls,  high  water  marks,  points  that  will 
define  the  stream  bed  at  the  bridge  and  points  along  the  banks 
of  the  stream  above  and  below  the  bridge. 

Some  engineers  prefer,  in  obtaining  cross-section  levels,  to 
run  a  line  of  profile  levels  with  the  instrument  on  the  transit 
line,  and  to  work  up  the  cross-section  levels  by  means  of  a 
hand  level. 

STAKING  GRADES.  Two  methods  of  staking  grades  are  in 
common  use.  One  method  is  to  drive  stakes  at  the  time  the 


70  ELEMENTS   OF  HIGHWAY  ENGINEERING 

survey  is  made.  The  ground  elevations  at  the  stakes  and  ele- 
vations on  tops  of  the  stakes  are  taken.  The  stakes  are  driven 
on  each  side  of  the  transit  line  far  enough  away  so  that  they 
will  not  be  disturbed  during  construction.  Along  tangents  the 
stakes  are  placed  at  intervals  of  either  50  or  100  feet.  On 
curves  they  may  be  spaced  as  close  as  25  feet,  depending  upon 
the  length  and  nature  of  the  curve.  When  the  grade  of  the  road 
has  been  established,  the  grade  elevations  at  the  stations  where 
the  stakes  are  driven  can  be  determined  in  the  office.  The 
difference  in  height  between  the  established  grade  and  the  tops 
of  the  stakes  is  recorded  on  a  sheet,  which  is  sent  to  the  inspector 
on  the  work,  who  is  thus  able  to  define  the  grade.  In  the  other 
method,  stakes  are  not  driven  until  after  the  grade  has  been 
determined  in  the  office.  The  stakes  are  then  driven  as  before 
and  notches  are  cut  on  the  stakes  at  grade  or  some  even  foot 
above  or  below  grade. 

SETTING  SLOPE  STAKES.  Slope  stakes,  defining  the  ends 
of  the  slopes,  should  be  set  where  the  cuts  or  fills  are  heavy. 
The  position  of  slope  stakes  can  be  most  easily  determined  by 
measuring  the  distances  on  the  plotted  cross-sections  from  the 
finished  line  to  the  edge  of  the  slope.  These  same  distances 
can  then  be  laid  off  in  the  field  at  their  respective  stations.  If 
the  work  is  through  a  rough  country,  and  no  cross-sections  had 
been  plotted,  the  slope  stakes  would  be  set  by  instruments  in 
the  field  as  in  railroad  work. 

Final  Surveys.  In  some  cases  it  is  essential  to  make  a 
survey  of  the  work  after  completion  before  making  the  final 
payment  for  the  roadway,  grading,  fencing,  culverts,  etc.  The 
methods  of  making  such  a  survey  are  the  same  as  those 
described.  The  information  desired  is  similar  in  character  to 
that  obtained  on  the  first  survey  except  that  it  refers  to  the 
finished  work. 

MAPPING  ROAD  SURVEYS 

THE  PLAN.  The  survey  plan  may  be  plotted  on  a  con- 
tinuous roll  of  detail  paper  in  one-mile  lengths  or  on  standard 
size  sheets.  The  transit  line  is  first  laid  out  on  the  sheet.  This 


SURVEYING,   MAPPING  AND  DESIGN 


71 


may  be  plotted  by  several  methods.  One  is  to  compute  the  co- 
ordinates of  the  several  intersecting  points  of  the  tangents  with 
reference  to  one  of  the  tangents  as  a  base  line.  (See  Fig.  16.) 
The  plotting  should  be  carefully  done,  and  as  a  check  the  angles 
between  the  tangents  should  be  read  with  a  protractor  and  the 
length  of  the  tangent  should  be  measured  between  the  points  as 
obtained  by  the  coordinates.  Another  method  which  is  quite  sim- 


C  e  9  Base  Line 


FIG.  16.     Coordinate  Method  of  Plotting  Transit  Line. 


FIG.  17.     Tangent  Method  of  Plotting  Transit  Line. 

ilar,  fully  as  accurate,  and  more  rapid,  since  it  eliminates  the  ne- 
cessity of  drawing  a  rectangular  system  of  coordinates,  is  the 
so-called  tangent  method  in  which  the  lines  are  run  out  and  the 
tangential  offsets  plotted  (see  Fig.  17).  In  this  case  the  pro- 
longation of  each  tangent  serves  as  a  base  from  which  the  tan- 
gential offset  is  plotted  to  obtain  the  next  intersection.  A  very 
common  method  is  to  plot  the  line  by  means  of  a  protractor 
and  scale.  It  is  impossible  to  plot  the  line  accurately  by  this 


72  ELEMENTS   OF  HIGHWAY  ENGINEERING 

method.  When  the  line  has  been  correctly  laid  out,  the  curves 
should  be  drawn  in  and  the  stations  should  then  be  marked  off 
on  the  line  and  the  survey  plotted  from  the  notes.  Conventional 
signs  can  be  adopted  for  the  detailed  topography. 

THE  PROFILE.  The  profile  may  be  plotted  below  the  plan 
at  the  bottom  of  the  sheet.  The  ground  line  of  the  profile 
should  represent  the  profile  of  the  original  surface  on  the  pro- 
posed center  line  of  road.  If  the  transit  line  corresponds  with 
the  proposed  center  line,  the  elevations  taken  on  the  transit 
line  will  be  the  ones  used;  otherwise,  the  center  line  elevations 
will  have  to  be  obtained  from  the  cross-sections.  Culverts, 
bridge  openings,  elevations  of  car  rails  adjacent  to  the  improved 
surface,  manholes,  curbs,  corner  boards  of  houses,  etc.,  should 
also  be  plotted  on  the  profile,  so  that,  when  the  grade  is  deter- 
mined, all  the  necessary  information  will  be  at  hand.  Some- 
times the  profile  is  plotted  on  translucent  profile  paper  such  as 
is  used  in  railroad  work.  Time  will  be  saved  if  this  is  done, 
since  it  will  not  be  necessary  to  draw  a  base  line  and  erect  verticals 
from  it. 

THE  CROSS-SECTIONS.  The  cross-sections  should  be  plotted 
either  on  cross-section  or  profile  paper.  The  scale  used  should 
be  as  much  as  >^-inch  to  the  foot,  since  the  estimate  of  cut  and 
fill  is  made  from  these  cross-sections,  and  the  use  of  a  large 
scale  makes  practicable  the  satisfactory  determination  of  areas. 

In  some  States,  where  the  engineering  force  is  large  and  the 
drawings  are  made  at  a  central  office,  it  is  essential  for  each 
engineer  in  charge  to  have  a  copy  of  the  plans.  This  is  most 
readily  accomplished  by  making  blue-prints  of  the  original 
drawings. 

SURVEYS  FOR  CITY  STREETS 

GENERAL  SCOPE  OF  THE  WORK.  As  streets  are  closely  re- 
lated to  each  other  and  the  property  bounded  by  streets  is 
valuable,  any  inaccuracies  in  surveys  may  mean  extensive  and 
troublesome  litigation.  In  order  to  study  the  situation  intelli- 
gently and  to  draw  up  a  plan  for  a  street  system,  it  is  necessary 
to  make  a  topographical  survey  of  the  area,  which  will  include 


SURVEYING,   MAPPING   AND   DESIGN  73 

all  existing  streets,  monuments,  property  lines,  waterways,  con- 
tours, etc.  The  extreme  accuracy  required  makes  it  necessary 
to  use  methods  differing  materially  from  those  which  are  adapt- 
able for  roads.  Transits  which  are  graduated  much  finer  than 
those  used  in  road  surveying  must  be  used  in  running  the  tra- 
verses in  this  class  of  work.  A  transit  with  a  limb  divided  to 
read  at  least  30  seconds  and  preferably  20  or  10  seconds  will 
give  the  best  results.  The  tapes  used  should  be  standardized 
by  comparison  with  the  standards  at  Washington  or  elsewhere. 

THE  TRAVERSE.  It  is  first  necessary  to  project  lines  over 
the  area  from  which  the  existing  topography  can  be  taken. 
One  method  of  doing  this  is  by  means  of  closed  traverses.  Sec- 
ondary traverses  are  run  with  any  of  the  sides  of  the  first  traverse 
as  a  base.  A  third  system  of  traverses  might  be  run  from  the 
second,  and  so  on  until  sufficient  lines  were  obtained  to  fully 
cover  the  area.  This  method  involves  some  inaccuracies,  how- 
ever, since  in  balancing  the  traverses  a  local  error  is  distributed 
throughout  the  entire  traverse. 

The  following  method  is  more  accurate.  The  United  States 
Coast  and  Geodetic  Survey  has  made  triangulation  surveys  of 
many  of  the  States  of  this  country.  Enough  points  on  the  sys- 
tem may  generally  be  found  within  the  city  limits  to  furnish  a 
triangulation  system  on  which  the  rest  of  the  work  can  be  based. 
The  triangulation  work  should  be  done  with  the  utmost  refine- 
ment and  the  points  established  should  be  permanently  monu- 
mented.  Points  on  the  triangulation  system  can  then  be  con- 
nected by  traverse  lines,  and  the  accuracy  of  each  traverse 
definitely  determined  by  calculation.  The  detailed  topography 
is  filled  in  from  these  traverse  lines  which  should  be  chosen  so 
as  to  facilitate  this  part  of  the  work. 

LEVELS.  Bench-marks  should  be  established  by  running 
closed  circuits  of  precise  levels.  The  level  datum  generally 
taken  is  mean  low  tide. 

MONUMENTING  THE  LINES.  The  topographical  survey  when 
completed  is  mapped.  With  the  aid  of  these  maps  a  design 
of  the  street  system  can  be  made.  The  location  of  the  monu- 
ments can  then  be  computed  and  their  position  established 


74  ELEMENTS   OF  HIGHWAY  ENGINEERING 

in  the  field.  Monuments  of  a  permanent  character  should  be  set 
in  the  sidewalk  at  a  certain  distance  out  from  the  property  line, 
so  that  they  will  always  be  intervisible  and  readily  accessible. 

SURVEY  FOR  GRADING.  When  a  street  has  once  been  cor- 
rectly monumented  a  detailed  survey  of  the  street  can  be  made 
previous  to  the  proposed  improvement.  The  transit  line  can 
be  referenced  in  with  the  existing  monuments.  Houses  and 
other  topography  should  be  located  by  some  accurate  method, 
such  as  by  angles  and  distances.  The  cross-section  levels  can 
be  taken  by  the  same  general  methods  as  outlined  in  road  sur- 
veying, except  more  accurate  work  is  required.  The  center  line 
grade  is  staked  in  the  same  manner  as  previously  described. 

STAKING  CURBS  AND  GRADES.  There  are  two  methods  that 
are  commonly  used  in  staking  out  curbs.  In  one  the  stakes 
are  driven  to  one  side  on  an  offset  defining  the  line  of  the  curb, 
and  the  tops  of  the  stakes  are  made  to  conform  to  the  grade 
of  the  curb.  In  the  other  method  the  stakes  are  driven  on  a 
line  as  before  with  their  tops  flush  with  the  ground  and  a  sheet 
of  instructions  is  furnished  which  gives  the  distance  above  or 
below  the  top  of  the  stake  to  the  grade  of  the  curb.  Curbs 
and  gutters  are  usually  constructed  in  advance  of  the  street 
pavement.  The  crown  and  grade  of  the  pavement  may  be  regu- 
lated by  setting  lines  of  stakes  transversely  to  the  street  at 
intervals  sufficiently  close  to  define  the  desired  shape  of  the 
surface.  In  the  case  of  wide  streets,  street  intersections,  and 
public  squares,  it  is  advisable  to  use  this  method.  On  the 
narrow  streets,  however,  the  engineer  may  be  furnished  with  a 
grade  sheet,  based  on  the  elevations  of  the  tops  of  curbs,  show- 
ing the  relative  elevations  of  all  controlling  points  along  and 
across  the  roadway. 

MAPPING  STREET  SURVEYS 

TOPOGRAPHICAL  MAP.  The  topographical  survey  of  the 
city  should  be  plotted  by  the  system  of  rectangular  coordinates. 
On  this  plan  should  be  shown  all  of  the  triangulation  points, 
traverse  points,  as  well  as  all  the  topography.  Such  a  map 
might  be  made  to  a  scale  of  200  feet  to  the  inch.  With  this 


SURVEYING,   MAPPING  AND  DESIGN  75 

scale  it  is  possible  to  represent  a  large  area  on  a  sheet  of  prac- 
ticable size  and  have  the  topography  in  sufficient  detail  so  that 
an  intelligent  study  of  the  street  plan  as  a  whole  can  be  made. 
Sectional  plans  can  be  made  of  any  portion  of  this  map  to  as 
large  a  scale  as  is  desired  when  working  out  the  details  of  any 
particular  locality.  If  plane  tables  are  used  on  the  survey,  the 
topography  may  be  plotted  in  the  field.  In  such  a  case  a  scale 
as  large  as  50  feet  to  the  inch  should  be  used.  The  plans,  pro- 
files, and  cross-sections  of  the  individual  streets  are  plotted  in 
a  manner  similar  to  that  described  for  roads. 

DESIGN 

DEVELOPMENT  OF  HIGHWAY  SYSTEMS.  The  several  classes 
of  highway  systems  may  be  designated  as  follows:  national, 
state,  county,  town,  city,  park,  and  estate.  National,  county, 
and  town  highway  systems  are  governed  by  the  same  general 
principles  as  those  of  states,  and  estate  highway  systems  are 
very  similar  to  those  of  parks,  hence  a  consideration  of  state, 
city,  and  park  systems  will  cover  all  cases. 

State  Highway  Systems.  Many  of  the  States  in  this  country 
lack  a  broad,  comprehensive,  and  connected  system  of  highways 
due  to  several  reasons.  Some  States  which  construct  roads 
under  a  state-aid  plan  are  handicapped  by  the  fact  that  any 
town  or  county,  which  is  able  to  subscribe  its  share  of  the  money, 
can  demand  state  aid  for  the  construction  of  any  piece  of  road 
within  its  borders,  regardless  of  its  location.  The  result  of  this 
form  of  legislation  is  the  construction  of  innumerable  short  sec- 
tions of  road  throughout  the  State.  These  roads,  in  many  cases, 
are  only  of  local  benefit,  sometimes  even  restricted  to  the  prop- 
erty owners  residing  adjacent  to  them.  There  are  some  States, 
on  the  other  hand,  that  have  adopted  a  connected  system  of 
roads  which,  when  built,  will  make  all  parts  of  the  State  and 
its  large  centers  readily  accessible. 

The  design  of  a  system  of  state  trunk  highways  is  simplified 
if  a  comprehensive  topographical  map  of  the  State  is  at  hand, 
such  as  is  made  by  the  United  States  Coast  and  Geodetic 
Survey.  If  such  maps  are  not  obtainable,  a  map  showing  sim- 


76  ELEMENTS   OF  HIGHWAY  ENGINEERING 

ply  the  roads  in  plan  can  be  used,  but  with  the  latter  the  study 
cannot  be  made  in  as  satisfactory  a  manner  except  by  doing  a 
large  amount  of  reconnoissance  work.  The  interstate  and  intra- 
state  trunk  lines,  the  interurban  trunk  lines,  and  popular  routes 
of  travel  should  first  be  laid  out.  Information  should  be  ob- 
tained from  the  officials  in  the  adjoining  States,  relative  to  the 
main  roads  in  those  States,  so  that  the  systems  in  the  two  States 
may  be  connected.  The  intrastate  highways  can  next  be  added 
to  the  system.  These  highways  pass  through  towns  and  con- 
nect towns  situated  within  a  few  miles  of  each  other.  Finally,  to 
the  system  of  trunk  highways,  there  should  be  added  the  feeders 
which  will  develop  the  commercial,  industrial,  and  agricultural 
resources  of  every  part  of  the  State.  Before  deciding  to  include 
any  section  of  road  in  the  system,  a  general  idea  should  be 
obtained  as  to  the  practicability  of  its  construction  at  a  reason- 
able cost,  and  it  should  be  ascertained  if  the  road  is  the  best  one 
to  be  built  from  the  standpoint  of  the  welfare  and  development 
of  the  communities  through  which  it  passes. 

City  Highway  Systems.  The  streets  in  the  older  portions 
of  many  large  cities  have  practically  the  same  lines  to-day  as 
in  the  first  years  of  the  cities'  development.  As  the  cities  grew, 
the  need  for  some  systematic  plan  of  street  development  was 
realized.  The  result  is  that  in  the  older  portions  of  some  cities 
the  streets  will  be  found  to  be  tortuous  and  narrow,  while  in 
the  more  recently  developed  portions  the  evidence  of  a  sys- 
tematic plan  is  apparent. 

A  street  plan  is  not  well  designed  unless  the  plan  is  made 
to  fit  the  topography  and  unless  proper  care  is  taken  of  the 
drainage.  Topographical  conditions  will  sometimes  preclude 
the  use  of  a  uniform  rectangular  system  if  easy  grades  are  to 
be  obtained.  The  history  of  the  growth  and  development  of 
large  cities  should  be  carefully  studied,  since  it  is  only  from 
these  examples  that  we  can  predict  what  future  conditions  may 
impose.  A  suburb  at  the  present  time  may  in  a  few  years  be- 
come an  important  part  of  the  city,  and  the  street  plan  should 
be  designed  on  such  comprehensive  lines  that  provision  is  made 
for  growth. 


SURVEYING,   MAPPING  AND   DESIGN 


77 


The  Rectangular  Plan.  The  rectangular  block,  system,  of 
which  New  York  City  is  a  good  example,  has  been  used  in 
many  cities  where  topographical  conditions  would  permit.  (See 


Courtesy  of  Mr.  Nelson  P.  Lewis. 

FlG.  1 8.     Street  Plan  of  New  York  City. 

Fig.  1 8.)  Such  a  system,  however,  if  entirely  devoid  of  diagonal 
streets  cutting  across  the  rectangular  plan,  does  not  accommo- 
date the  traffic  to  the  best  advantage  and  renders  very  little 
opportunity  to  improve  the  appearance  of  a  city.  Diagonal 


Courtesy  of  Mr.  Nelson  P.  Lewis. 

FIG.  19.     Street  Plan  of  Moscow. 

streets  radiating  from  the  city  center  to  large  public  squares, 
and  from  thence  to  the  outskirts,  enable  the  traffic  to  move 
from  one  part  of  the  city  to  another  with  the  greatest  despatch, 


78  ELEMENTS   OF  HIGHWAY  ENGINEERING 

and  tend  to  relieve  the  congestion  of  traffic  that  might  other- 
wise occur.  The  squares  and  centers  afford  a  location  for  the 
erection  of  beautiful  public  buildings,  the  diagonal  streets  leading 
into  the  square  making  a  fitting  approach  to  such  structures. 

The  Circumferential  Plan.  The  systems  of  many  European 
cities,  which  are  pointed  to  as  examples  of  comprehensive  street 
plans,  besides  having  a  rectangular  plan  intercepted  by  diagonal 
streets,  have  so-called  circumferential  streets  which  roughly  en- 
circle the  city.  This  is  well  illustrated  by  the  street  plans  of 
such  cities  as  Berlin,  Vienna,  Paris,  and  Moscow.  (See  Fig.  19.) 

Park  Highway  Systems.  An  ideal  park  system  for  any  city 
or  community  would  be  one  in  which  all  of  the  spaces  reserved 
for  parks  are  connected  with  scenic  boulevards.  In  this  country 
the  great  benefit  which  may  be  derived  from  parks  does  not 
seem  to  have  been  appreciated  until  recently.  Now,  however, 
many  of  the  States  and  cities  are  striving  to  take  advantage  of 
their  present  opportunities  in  this  direction.  Many  of  the  parks 
will  be  found  on  the  outskirts  of  the  larger  cities,  since  places 
which  still  retain  their  natural  beauty  can  only  be  acquired  in 
such  localities.  To  accommodate  different  sections  of  the  city 
and  to  allow  for  future  growth,  several  such  parks  should  be 
developed,  or  at  least  the  reservation  of  land  should  be  made  for 
this  purpose.  The  different  parks  may  be  connected  by  boule- 
vards and  drives,  which,  if  designed  in  the  proper  manner 
and  with  proper  aesthetic  effect,  become  a  part  of  the  parks 
themselves. 

The  design  of  the  highways  of  the  system  is  not  difficult. 
Distance,  alignment,  and  grade  are  not  of  so  much  importance 
as  in  the  case  of  a  highway  taking  both  a  pleasure  and  a  com- 
mercial traffic.  Particular  emphasis  should  be  given  to  the 
aesthetic  possibilities  of  the  highways.  This  may  sometimes 
involve  entirely  new  layouts,  such  as  roads  along  the  banks  of 
a  river,  the  seashore,  or  across  some  area  the  natural  environment 
of  which  is  especially  beautiful. 

SCOPE  OF  HIGHWAY  DESIGN.  A  complete  design  of  a  given 
highway  comprises  the  consideration  of  the  following  factors: 
relation  to  the  highway  system,  location,  width,  grade,  align- 


SURVEYING,   MAPPING  AND  DESIGN  79 

ment,  drainage,  foundation,  crown,  type  of  surface,  apd  estimate 
of  cost. 

Location.  The  most  economical  and  suitable  location  of  a 
highway  should  be  considered  before  it  is  improved.  At  this 
period  in  the  development  of  a  highway  no  expensive  improve- 
ments, such  as  grading,  drainage,  foundations,  pavement,  and 
bridges  stand  as  obstacles  to  the  proposed  change  of  a  poor 
location  and,  furthermore,  a  suitable  width  and  right  of  way 
on  a  relocation  may  be  secured  at  the  minimum  expense.  Meth- 
ods of  securing  rights  of  way  vary  in  the  several  States,  dependent 
upon  their  statutes.  Some  States  have  laws  which  permit  high- 
ways to  be  located  and  constructed  before  landowners  are  paid 
for  the  rights  of  way.  If  dissatisfied  with  the  final  award  of 
the  highway  authorities,  the  owners  may  appeal  to  the  proper 
court.  This  procedure  is  based  on  the  principle  that  the 
expeditious  construction  of  a  highway  in  a  desirable  location  is 
advantageous  to  the  people  as  a  whole.  As  a  general  proposi- 
tion, the  land  is  acquired  economically  under  this  method.  In 
those  States  where  rights  of  way  must  be  paid  for  before  the 
highway  is  constructed,  the  prices  demanded  by  owners  are  in 
many  cases  exorbitant,  and,  in  addition,  the  overhead  charges 
are  frequently  very  large  as  expensive  legal  and  engineering  work 
is  often  required  before  adjustments  are  completed. 

In  connection  with  the  location  of  new  highways  or  the  re- 
location of  old  highways,  the  following  factors  should  be  given 
careful  consideration:  (i)  the  highway  should  develop  to  a 
maximum  extent  the  commercial,  agricultural,  and  industrial 
interests  of  the  community;  (2)  the  highway  should  serve,  the 
largest  number  of  people  practicable;  (3)  the  amount  of  cut 
and  fill  should  be  reduced  to  a  minimum;  (4)  good  natural 
drainage  should  be  secured  and  .longitudinal  surface  drainage 
obtained  by  establishing  a  minimum  grade  of  0.5  per  cent;  (5) 
other  conditions  permitting,  natural  stable  foundations  should 
be  utilized  and  such  natural  foundations  as  low  swampy  ground, 
locations  subject  to  overflow  and  the  stratigraphic  conditions 
where  there  is  a  tendency  of  one  stratum  of  soil  to  slide  or  slip 
upon  another  should  be  avoided;  (6)  grades  should  be  as  low 


80  ELEMENTS   OF  HIGHWAY  ENGINEERING 

as  practicable,  as  the  maximum  grade  limits  the  amount  of  the 
load  which  can  be  moved  over  a  highway;  (7)  locations  en- 
circling hills  should  be  substituted  for  steep  inclines  over  sum- 
mits; (8)  if  the  topography  is  such  that  there  is  a  continual 
rise,  the  grade  line  should  not  have  a  descending  grade;  (9)  long 
easy  curves  should  be  substituted  for  sharp  curves;  (10)  in 
mountainous  regions  highways  should  be  built  on  side  slopes 
and  avoid,  if  practicable,  northern  exposures  and  locations  near 
stream-beds;  (u)  dangerous  railroad  crossings  should  be  avoided. 

Widths.  A  width  should  be  selected  which  will  not  only 
accommodate  the  present  traffic,  but  also  be  sufficient  to  allow 
for  a  reasonable  future  development.  In  the  case  of  streets, 
provisions  for  light  and  air,  room  for  subsurface  structures  and 
car-tracks,  as  well  as  accommodations  for  the  traffic  of  vehicles 
and  pedestrians  must  be  considered.  The  width  of  roads  is 
based  mainly  upon  the  amount  of  vehicular  traffic.  In  the  case 
of  park  highways  the  basis  for  design  is  the  same  except  that 
the  proper  aesthetic  treatment  of  the  highway  may  warrant 
using  a  width  not  otherwise  justifiable. 

Width  of  Streets.  In  wholesale  districts  where  the  pedestrian 
travel  is  light,  the  sidewalk  widths  can  be  reduced  and  the 
width  thus  obtained  put  into  the  carriageway.  A  large  com- 
mercial truck  backed  up  against  the  curb  will  occupy  a  length 
of  about  13^/2  feet.  A  truck  on  either  side  of  the  street  in  this 
position  would  therefore  occupy  27  feet.  The  width  out  to  out 
of  the  ordinary  commercial  motor-truck  is  between  6  feet  and  8 
feet  6  inches.  To  provide  for  the  easy  passage  of  two  lines  of 
vehicles  between  those  backed  up  against  the  curbs  would  thus 
require  an  additional  width  of  carriageway  of  about  17  feet, 
which  would  make  the  total  width  of  carriageway  about  44  feet. 
For  streets  in  retail  business  districts  the  pedestrian  traffic  is  of 
more  importance  and  the  sidewalks  should  be  given  adequate 
width.  In  residential  districts  a  carriageway  of  from  30  to  36 
feet  is  generally  ample.  Where  a  residential  street  is  subjected 
to  a  light  local  traffic  consisting  principally  of  delivery  wagons 
and  pleasure  vehicles,  there  is  no  need  for  a  roadway  wider  than 
20  feet.  There  are  several  advantages  in  favor  of  the  smaller 


SURVEYING,   MAPPING  AND  DESIGN  81 

width.  Assuming  that  the  distance  between  property  lines  is 
60  feet  and  a  2o-foot  roadway  is  constructed,  40  feet  is  left 
available  for  sidewalks  and  parking  spaces.  Allowing  a  width 
of  12  feet  for  each  sidewalk,  a  parking  space  could  be  constructed 
beyond  the  sidewalk  on  each  side  8  feet  in  width.  This  space, 
if  properly  treated,  would  add  greatly  to  the  appearance  of  the 
street.  By  reducing  the  width  of  roadway  the  first  cost  of  con- 
struction and  later  maintenance  costs  are  materially  reduced. 
The  width  of  20  feet  is  ample  for  two  teams  to  pass  or  one  to 
pass  when  the  other  is  backed  against  the  curb.  The  parking 
spaces  would  be  available  for  the  location  of  underground  services, 
and  thus  frequent  disturbances  to  the  roadway  could  be  avoided. 
Street  widths  are  generally  stated  as  the  distance  between  prop- 
erty lines.  The  width  taken  by  each  sidewalk  in  city  streets  is 
from  one-fourth  to  one-fifth  the  total  distance  between  property 
lines,  although  this  may  be  reduced  in  some  instances. 

Width  as  A/ected  by  Car  Tracks.  Wherever  possible,  it  is 
best  to  provide  a  trackway  for  cars  which  is  separated  from 
the  roadway  by  a  barrier  or  parking  space.  Where  trackways 
have  to  be  built  within  the  limits  of  the  roadway,  the  width  of 
the  street  will  determine  whether  it  is  best  to  locate  them  at  the 
sides  of  the  street  or  to  put  them  in  the  center.  This  subject 
is  considered  in  detail  in  Chapter  XXI.  A  great  deal  of  the 
passenger  traffic  in  the  future  may  be  carried  on  motor-buses. 
The  use  of  this  type  of  public  conveyance  will  eliminate  the  car 
tracks  from  the  roadway. 

W-idth  as  A/ected  by  Subsurface  Structures.  Ample  provision 
must  be  made  for  the  location  of  subsurface  structures.  In 
business  districts  these  structures  become  very  much  congested. 
Sewers,  water  and  gas  pipes,  conduits  for  telegraph  and  telephone 
wires,  steam  and  hot  water  pipes,  refrigerating  pipes,  and  tunnels 
are  commonly  found  in  our  largest  cities.  The  space  under- 
neath the  sidewalk  from  the  property  line  to  the  curb  line  and 
extending  to  the  sidewalk  level  in  many  streets  of  the  business 
districts  of  American  cities  is  utilized  as  a  vault  by  the  property 
owner.  This  prevents  using  the  sidewalk  width  for  the  accom- 
modation of  subsurface  structures  and  makes  it  necessary  to 


82  ELEMENTS   OF  HIGHWAY  ENGINEERING 

place  them  within  the  carriageway.  It  is  evident  that  the  in- 
terests of  the  roadway  will  be  best  served  by  eliminating  from 
it  all  pipes  which  are  liable  to  be  disturbed  to  any  extent.  The 
expense  entailed  in  constructing  pipe  galleries  on  either  side  of 
the  street  for  the  accommodation  of  these  structures  is  so  great 
that  it  becomes  prohibitive  except  in  very  special  cases.  This 
topic  will  be  further  considered  in  Chapter  XXI. 

Width  of  Roads.  Carriageways  of  roads  which  only  take  a 
horse-drawn  vehicle  '  traffic  can  be  made  narrower  than  those 
which  are  subjected  to  both  horse-drawn  and  motor-car  traffic. 
In  the  former  case  a  width  of  14  to  1 6  feet  gives  sufficient  clear- 
ance between  two  passing  teams.  The  width  out  to  out  of  the 
average  touring-car  is  about  six  feet,  while  motor  trucks  are 
made  as  wide  as  8  feet  6  inches.  A  wider  roadway  is  required 
than  for  the  horse-drawn  vehicle  traffic  in  order  to  allow  the 
machines  to  pass  each  other  at  a  fair  rate  of  speed  with  the 
proper  clearance  and  still  keep  on  the  improved  surface.  For 
interstate  and  intrastate  highways  a  width  of  improved  surface 
of  1 8  to  20  feet  would  probably  be  none  too  great,  while  a  width 
of  14  to  1 6  feet  would  be  ample  for  those  roads  which  act  as 
feeders  to  the  classes  just  mentioned,  the  smaller  width  to  be 
used  only  in  case  of  very  light  traffic.  It  is  unfortunate  that 
some  authorities,  charged  with  the  design  of  state  trunk  high- 
ways subjected  to  a  mixed  traffic,  have  adopted  a  width  of  road- 
way of  only  12  feet.  (See  Fig.  20.)  In  England  the  carriage- 
ways of  main  roads  are  made  from  16  to  22  feet  wide,  while  those 
of  the  national  roads  in  France  are  made  24  feet  wide.  (See  Fig. 
21.)  There  are  many  existing  roads  which  have  a  right  of  way 
much  wider  than  is  necessary.  In  acquiring  a  strip  of  land  for 
a  new  location  a  width  of  30  feet  on  each  side  of  the  center  line 
is  ordinarily  sufficient.  The  shoulders  of  roads  make  a  suitable 
place  for  the  location  of  pipes.  There  are  places,  however, 
where  the  pipes  will  have  to  be  located  within  the  carriageway. 
In  such  cases,  the  best  location  of  either  the  water  or  gas  pipes 
is  at  one  side  of  the  road  so  that  work  incident  to  these  services 
will  not  interfere  with  the  traffic. 

Width  of  Park  Highways.    The  same  general  principles  set 


FIG.  20.     State  Highway.     Improved  Surface  12  feet  Wide. 


FIG.  21.     National  Road,  France.     Width  of  Roadway,  24  feet. 


84  ELEMENTS   OF  HIGHWAY  ENGINEERING 

forth  relative  to  the  width  of  streets  and  roads  apply  to  the 
highways  of  parks.  It  has  been  previously  mentioned,  however, 
that  the  width  adopted  is  also  affected  by  the  consideration  of 
aesthetics.  There  is  no  set  of  rules  which  can  be  given  covering 
the  relation  of  width  to  aesthetics,  since  the  problem  is  one 


,    T 

\     *      \ 
\   1  Walk.       1     J                    Parkway 
1   I               I 

Planting  Space 

. 

FlG.  22.     Typical  Section  of  Park  Highway.     Massachusetts  Metropolitan 
Park  Commission. 

largely  influenced  by  local  conditions.  Many  park  commissions 
have  adopted  standard  widths  to  be  used  under  different  con- 
ditions. A  typical  section  is  shown  in  Fig.  22. 

Grades.  In  practice  the  maximum  grade  may  be  governed 
by  the  loads  to  be  hauled  over  a  given  highway,  but  in  many 
localities  a  maximum  rate  of  grade  is  established,  which  is  never 
exceeded  except  when  the  environments  and  the  consideration 
of  cost  make  it  advisable  to  use  a  steeper  grade.  All  classes  of 
motor  vehicles  are  so  designed  that  they  can  climb,  without 
difficulty,  practically  any  grade  which  would  be  built  for  horse- 
drawn  vehicles,  hence,  only  horse-drawn  vehicles  have  to  be 
considered.  A  horse  can  exert  a  pull  of  120  pounds  when  work- 
ing steadily,  and  for  a  short  period  this  pull  may  be  increased 
to  practically  500  pounds.  As  the  grade  increases,  the  load  a 
horse  can  pull  decreases  very  rapidly.  For  instance,  on  a  6  per- 
cent grade  a  horse  can  readily  pull  only  about  one-half  as  much 
as  on  the  level;  on  a  10  percent  grade,  only  one-fourth  as  much. 

The  grade  must  be  established  so  as  not  to  cause  damage 
to  the  adjoining  property  and  so  as  to  best  accommodate  inter- 
secting streets  or  roads.  Proper  drainage  and  foundations  should 
receive  consideration  in  grade  design.  In  the  case  of  roads, 
particularly,  it  is  frequently  necessary  to  raise  considerably  the 


SURVEYING,   MAPPING  AND  DESIGN  85 

existing  grade  in  order  to  obtain  a  satisfactory  foundation.  A 
saving  may  be  effected  by  taking  advantage  of  an  old  surface 
as  a  foundation,  the  new  grade  being  established  so  as  to  dis- 
turb the  old  roadway  as  little  as  possible.  Although  it  is  of 
material  advantage  to  obtain  a  grade  which  will  make  the  cuts 
and  fills  balance,  or  in  other  words,  preclude  the  necessity  of 
any  borrow  on  the  work,  still  it  is  obvious  that  many  times 
other  considerations  are  of  far  greater  importance.  The  ad- 
visability and  economy  of  balancing  cuts  and  fills  from  the 
standpoint  of  grading  can  only  be  ascertained  by  comparing 
the  cost  of  possible  overhaul,  in  moving  the  earth  from  one 
point  on  the  road  to  another,  with  the  cost  of  borrow  at  some 
nearer  point. 

Maximum  Grades.  Grades  as  high  as  20  percent  are 
found  in  mountainous  districts.  Many  of  the  State  High- 
way Departments  never  use  grades  over  7  percent.  Within 
the  cities  the  grades  usually  follow  quite  closely  the  general 
topography  of  the  earth's  surface,  and  hence  the  problem,  in 
this  case,  is  to  provide  a  surface  that  will  be  suitable  to  the 
traffic.  In  the  Borough  of  The  Bronx,  New  York  City,  the 
grade  of  sheet  asphalt  is  usually  limited  to  3  percent,  wood 
block  to  3  percent,  asphalt  block  to  6  percent,  vitrified  brick 
to  5  percent,  while  granite  block  has  been  laid  on  grades  of 
13  percent. 

Minimum  Grades.  The  minimum  rate  of  grade  varies  in- 
versely with  the  smoothness  of  a  roadway  surface.  If  the  road- 
way surface  of  a  broken  stone  road  is  well  maintained  and  a 
good  fall  is  given  to  the  ditches  at  the  sides,  there  is  no  reason 
why  a  flat  grade  cannot  be  used  for  a  short  length.  The  mini- 
mum grade  of  streets  is  important  from  the  standpoint  of  drain- 
age. It  is  possible  in  flat  places  to  make  the  curbs  level  and 
to  obtain  the  grade  by  increasing  the  depth  from  the  gutter  to 
the  top  of  the  curb. 

Drawing  the  Grade.  The  ground  line  of  the  profile  should 
be  carefully  studied  as  certain  limiting  points  on  the  grade 
line  may  be  established  by  giving  attention  to  the  considera- 
tions enumerated  above.  Grade  lines  can  then  be  drawn  in 


86 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


between  these  points  by  trial  until  a  final  grade  is  determined 
which  will  best  fit  the  conditions. 

On  roads  it  is  customary  to  change  the  grade  at  some  station 
which  is  a  multiple  of  50  or  100  feet.  This  is  purely  a  matter 
of  convenience,  however,  in  that  it  facilitates  the  grade  com- 


FIG.  23.     Sketch  Showing  Representation  of  Finished  Grade  Line. 

putations  when  the  grade  has  to  be  figured  for  every  5o-foot 
station.  The  grade  is  shown  only  on  the  profile  of  the  drawing. 
Elevations  are  written  for  all  stations  of  vertical  curves  and  for 
all  points  denoting  a  change  of  grade.  The  rates  of  grade  are 
written  along  the  grade  line  where  it  is  uniform  for  a  distance 
of  100  feet  or  more.  Fig.  23  shows  the  original  ground  line 
and  the  finished  grade  line  and  represents  one  method  of  recording 
the  grade  on  the  plan. 

On  streets  it  is  customary  to  make  the  grade  a  straight  line 
between  the  intersecting  streets  unless  a  perfectly  flat  grade 
would  result,  in  which  case  it  is  usually  broken  to  provide 
for  drainage.  This  is  a  general  principle,  but  the  topog- 
raphy, cost  of  construction,  damage  to  abutting  property,  and 
the  general  appearance  of  the  street  may  prevent  its  adoption 
in  some  cases.  Furthermore,  it  will  sometimes  be  necessary  to 
make  slight  changes  in  the  grade  for  the  grade  table,  formed 
by  the  intersecting  streets,  in  order  to  provide  an  intersection 
that  will  not  only  look  well,  but  will  take  care  of  the  water  and 
be  safe  to  use.  The  grades  for  streets  should  be  established  and 
recorded  so  that  the  proper  grade  can  be  given  for  new  buildings 
and  other  structures  which  may  be  built  in  advance  of  the 
street  improvement. 


SURVEYING,    MAPPING  AND   DESIGN 


87 


Vertical  Curves.  In  order  to  avoid  the  abrupt  transition  from 
one  grade  to  another,  a  vertical  curve  is  put  in  at  the  grade 
intersections,  the  length  of  which  should  be  increased  as  the 
difference  between  the  rates  of  the  intersecting  grades  increases. 


FIG.  24.     Vertical  Curve. 

The  parabola  is  the  form  of  curve  which  is  most  generally  used. 
In  Fig.  24,  two  intersecting  grades  are  shown  by  the  lines  A  B 
and  B  C  and  the  vertical  curve  by  the  line  m  u  e  t  n. 

Design  of  Street  Intersections.    The  adjustment  of  grades  at 
street  intersections  is  sometimes  a  very  troublesome  problem. 


I  99.10 


99.10 


_ 

100.90 


100.90 


-6f»  A 


FIG.  25.     Elevations  at  Curb  Corners  from  Intersecting  Grades. 

The  grade  usually  required  to  be  established  by  ordinance  is 
that  of  the  center  of  the  street.  In  order  to  avoid  confusion 
the  grade  of  the  curb  corners  or  of  the  property  corners  should 
also  be  established.  An  examination  of  Fig.  25  will  show  the 
importance  of  recording,  not  only  the  elevation  of  the  inter- 


88  ELEMENTS   OF  HIGHWAY  ENGINEERING 

secting  centers  of  streets,  but  also  the  two  elevations  for  each 
curb  corner  and  for  each  property  corner. 

Curves.  In  the  design  of  roads,  subjected  primarily  to  horse- 
drawn  vehicle  traffic,  the  proper  radius  of  curve  would  depend 
principally  upon  the  overall  length  of  the  horses  and  wagon 
and  the  width  of  the  road.  It  has  been  found  that  to  permit 
a  vehicle  drawn  by  four  horses  to  keep  upon  a  1 2-foot  roadway 
requires  a  curve  having  an  inside  radius  of  about  100  feet.  In 
designing  a  road  that  takes  either  motor-car  traffic  alone  or  a 
combination  of  motor-car  and  horse-drawn  vehicle  traffic,  the 
safety  of  the  travelling  public  and  the  wear  of  the  roadway  must 
be  considered.  Sharp  curves  are  points  at  which  collisions  are 
very  liable  to  occur,  particularly  if  the  view  is  obstructed.  It 
is  natural  for  all  traffic  to  keep  to  the  inside  of  the  curve,  and 
in  the  case  of  the  motor  vehicles,  if  the  speed  is  not  brought 
down  to  about  ten  or  fifteen  miles  an  hour,  the  slew  of  the 
vehicles  as  they  pass  around  the  curve  tends  to  grind  out  the 
surface  of  the  roadway.  The  following  conclusion  was  adopted 
by  the  First  International  Road  Congress  held  in  Paris  in  1908: 
"The  radii  of  curves  should  be  as  great  as  possible,  164  feet  at 
least;  the  outside  of  curves  should  be  slightly  raised  but  so  as 
not  to  inconvenience  ordinary  vehicles;  no  obstructions  to  the 
view  should  be  allowed  at  curves."  Fig.  26  is  a  typical  layout, 
showing  the  widening  of  a  broken  stone  road  at  curves,  as  adopted 
by  the  Los  Angeles  County  Highway  Commission  in  1910.  A 
poor  design  is  shown  in  Fig.  27. 

Sharp  curves  on  streets  are  unavoidable,  since  a  rectangular 
block  system  always  forms  a  large  part  of  the  street  plan.  The 
radii  of  the  curves  at  the  corners  of  streets  will  generally  vary 
from  about  four  to  twelve  feet.  On  wide  streets  the  smaller 
radii  can  be  used,  whereas  on  streets  of  the  minimum  width 
the  corners  should  have  the  larger  radii  if  possible  in 
order  to  better  accommodate  vehicular  traffic  entering  the 
street. 

As  previously  stated  the  use  of  curves  on  a  park  system  of 
roads  is  desirable  from  the  aesthetic  standpoint.  For  instance, 
a  winding  road,  following  the  natural  contours  of  the  ground 


SURVEYING,   MAPPING  AND   DESIGN 


89 


90 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


along  some  lake  shore  or  river  bank,  tends  to  emphasize  the 
natural  beauties  of  the  surrounding  scenery. 

Cross-Sections  of  Roads  and  Streets.     The  general  form  of 


FIG.  27.     Example  of  Poor  Curve  Design. 


FIG.  28.     Standard  Road  Section.    New  York  State  Department  of  Highways. 


rg£  

FIG.  29.     Standard  Road  Section.     Massachusetts  Highway  Commission. 

the  cross-section  adopted  for  a  street  or  a  road  will  depend  upon 
its  location  and  the  material  of  which  the  roadway  is  constructed. 
Typical  cross-sections  adopted  by  two  State  Highway  De- 
partments are  shown  in  Figs.  28  and  29.      The   slope   of   the 


SURVEYING,    MAPPING  AND   DESIGN  •  91 

banks  depends  upon  the  kind  of  material  of  whfch  they  are 
composed.  As  ordinary  earth  in  a  dry  state  has  an  angle  of 
repose  of  i  on  i  ^,  this  slope  is  in  common  use  for  embankments 
and  cuts.  It  is  customary  in  many  States  to  carry  out  the 
shoulders  of  fills  less  than  4  feet  in  height  with  a  i  on  4  slope, 
which  practically  renders  unnecessary  the  use  of  a  guard-rail. 

Crowns.     The  crown  for  the  roadway  surface,  see  Fig.  30, 
is  composed  of  intersecting  planes  or  of  arcs  of  a  circular  or  para- 


. 


FIG.  30.     Cross-Section  of  Highway  Showing  Crown  of  Roadway. 

bolic  curve.  The  purpose  of  a  crown  is  to  readily  shed  the  water 
falling  on  it  without  causing  inconvenience  to  traffic.  It 
is  a  general  rule  that  the  smoother  the  surface  the  less  the 
requisite  amount  of  crown.  A  steep  crown  will  cause  traffic  to 
concentrate  on  the  center  of  the  carriageway  with  the  result 
that  the  surface  will  not  be  subjected  to  an  even  wear.  For 
surfaces  which  are  not  impervious,  such  as  earth  and  gravel 
roads,  it  has  been  customary  to  make  the  crown  on  steep  grades 
sharper  than  on  the  flat  grades  to  prevent  water  from  running 
down  the  center  of  the  road.  If  a  heavy  crown  is  used  on  a 
road  which  lies  on  a  steep  grade  and  has  a  smooth  surface,  it 
will  be  dangerous  for  the  traffic  under  certain  climatic  conditions. 
Crown  Formulas.  The  derivation  of  many  crown  formulas 


92  ELEMENTS   OF  HIGHWAY  ENGINEERING 

is  based  on  a  parabolic  curve.  Some  give  the  total  amount  of 
crown,  but  not  its  distribution,  whereas  in  others  the  amount 
of  crown  is  assumed  and  the  formula  gives  its  distribution. 
Most  formulas  do  not  take  the  grade  of  the  highway  into  ac- 
count or  make  allowance  for  the  different  kinds  of  pavements. 
The  following  formula,  deduced  by  Joseph  W.  Dare,*  is  given 
as  an  illustration  of  the  type  of  formula  used  in  cities  throughout 
the  United  States: 


6300  +  50  P2 

C  =  crown  in  inches  ;  P  =  longitudinal  grade  expressed  as  a  per- 
centage; W  =  width  of  roadway  in  inches. 

The  distribution  of  the  above  crown,  when  curbs  are  level, 

8  C 
is  obtained  by  the  formula  -—  -  =  d,  where  d  =  the  transverse 

grade,  expressed  as  a  percentage,  R  =  width  of  roadway  in  feet. 
In  the  following  diagram, 

T-  T  5-  f 

a  or  b  +_£_  =  the  elevation  at  A  or  D. 
iS 

a  or  b  -f_C_  =  the  elevation  at  B. 
12 

a  and  b  =  the  elevation  at  the  gutters,  expressed  in  feet  and 
hundredths.  In  the  diagram  it  is  shown  that  the  transverse 
slope  between  the  crown  and  quarter  point  is  just  one-half 
what  it  is  between  the  quarter  point  and  gutter. 

Drainage  and  Foundations.  The  results  of  the  preliminary 
examination  will  furnish  much  valuable  information  relative  to 
surface  and  subdrainage  and  the  foundation.  A  consideration 
of  these  subjects,  however,  will  be  given  in  full  in  Chapter  V. 

Selection  of  Type  of  Wearing  Course.  There  are  many  char- 
acteristics of  the  materials  used  and  the  methods  of  construction 

*  See  Trans.  Am.  Soc.  C.  E.,  Vol.  73,  page  225. 


SURVEYING,   MAPPING  AND  DESIGN  93 

employed  that  influence  the  selection  of  the  type,  of  road  or 
pavement.  This  subject  will,  therefore,  not  be  considered  further 
in  this  chapter,  although  it  is  an  important  part  of  the  design. 
The  comparison  of  different  types  of  roads  and  pavements  is 
considered  in  detail  in  Chapter  XIX. 

Estimates.  When  the  location,  width,  and  grade  of  the  high- 
way and  the  form  of  cross-section  have  been  adopted,  an  estimate 
can  be  made  of  the  amount  of  work  to  be  done  and  the  cost 
thereof.  Complete  estimates  cover  the  grading,  drainage,  founda- 
tion, wearing  course,  and  all  highway  structures. 


CHAPTER  V 

GRADING,  DRAINAGE,  AND  FOUNDATIONS 

GRADING 

OBJECT  OF  GRADING.  Grading  operations  are  used  in  the 
construction  of  all  highways,  and  may  be  classified  under  the 
headings:  excavation,  embankment,  and  subgrade.  The  meth- 
ods of  construction  of  cuts,  fills,  and  subgrades  with  various 
machines  are,  in  most  cases,  explained  later  in  this  chapter 
in  connection  with  the  descriptions  of  the  several  machines. 

EXCAVATION.  In  excavating  material  in  order  that  the  cross- 
section  of  a  highway  should  conform  to  the  desired  lines  and 
grades,  the  operations  vary  from  the  removal  of  a  small  amount 
of  material  in  surface  grading  to  excavations  of  many  feet  in 
depth.  Excavation  includes,  in  general,  grading  of  the  road- 
way, ditches,  and  side  slopes.  The  excavated  material  is  used 
to  fill  those  parts  of  the  highway  which  are  below  the  proper 
grades.  Surplus  excavation  is  used  in  many  cases  to  widen 
embankments  and  flatten  side  slopes. 

EMBANKMENT.  Before  the  construction  of  the  embank- 
ment is  begun,  trees,  large  roots,  brush,  and  other  objectionable 
material  within  the  entire  area  to  be  covered  by  the  fill  should 
be  removed.  Where  the  filling  is  less  than  about  two  feet  in 
depth,  all  vegetable  matter  should  be  removed  from  the  original 
surface.  These  requirements  are  necessary  in  order  to  secure 
an  embankment  free  from  soft  and  spongy  pockets.  If  stone 
filling  is  employed,  usually  the  stones  should  not  exceed  a  half 
cubic  foot  in  size  and  the  larger  stones  should  be  placed  in  the 
bottom  of  the  excavation.  No  large  stone  should  be  used  within 
six  inches  of  the  surface  of  the  subgrade  or  shoulders.  In  the  con- 
struction of  embankments  it  is  of  the  utmost  importance  that  the 
materials  should  be  thoroughly  compacted  in  order  to  avoid 

94 


GRADING,   DRAINAGE,   AND   FOUNDATIONS  95 

later  settlement.  In  order  to  accomplish  the  desired  result, 
the  material  to  form  the  embankment  should  be  deposited  in 
thin  layers,  not  over  twelve  inches  in  depth,  for  the  full  width 
of  the  embankment  and  thoroughly  compacted.  The  compaction 
is  accomplished  by  machines  and  loaded  wagons  used  in  grading 
operations  being  drawn  continually  over  the  embankment,  and 
by  rolling.  Many  engineers  have  obtained  the  best  results  by 
the  use  of  sectional  rollers  or  comparatively  light  rollers  on  thin 
layers  of  material.  In  the  construction  of  highways  on  side  hills 
it  is  advisable  to  stagger  or  roughen  the  material  of  the  hillside, 
in  order  to  form  a  mechanical  bond  between  the  material  of 
the  fill  and  the  surface  of  the  ground,  thus  guarding  against  the 
slipping  of  the  embankment. 

When  the  excavated  material  suitable  for  use  in  the  con- 
struction of  embankments  is  insufficient,  additional  material  is 
obtained  from  borrow  pits  or  other  sources.  In  cases  where  the 
haul  of  material  required  for  embankments  exceeds  a  given 
distance,  the  work  entailed  is  classified  as  overhaul.  If  this 
distance  is  2,000  feet,  payment  for  overhaul  would  be  based 
upon  a  rate  per  cubic  yard  for  each  100  linear  feet  greater  than 
2,000  feet  that  the  material  is  hauled. 

SIDE  SLOPES.  When  the  excavations  and  embankments  are 
on  roads,  one  of  the  most  important  details  of  construction  is 
the  formation  of  the  side  slopes  in  such  a  manner  that  the  cross- 
section  of  the  highway  will  practically  retain  its  form.  In  many 
cases,  in  order  to  avoid  washing  away  of  side  slopes  during 
heavy  rains,  the  slopes  of  both  excavations  and  embankments 
are  sowed  with  grass  seed  or  covered  with  sod.  For  all  prac- 
tical purposes,  earth,  sand,  and  gravel,  when  used  in  either 
excavation  or  embankment,  will  be  stable  if  the  side  slopes  are 
constructed  with  an  inclination  of  i  on  i^. 

SUBGRADE.  The  subgrade  consists  of  "the  upper  surface 
of  the  native  foundation  on  which  is  placed  the  road  metal  or 
the  artificial  foundation,  in  case  the  latter  is  provided."*  The 
subgrade  is  thoroughly  compacted  by  rolling  to  conform  to  the 

*  Dec.,  1914  Proceedings,  Am.  Soc.  C.  E.,  page  3018. 


96  ELEMENTS   OF  HIGHWAY  ENGINEERING 

lines  and  grades.  All  muck,  quicksand,  soft  clay,  or  spongy 
material,  which  will  not  consolidate  under  the  roller,  is  removed 
to  such  depth  as  is  necessary  and  the  space  is  refilled  with  suit- 
able materials  from  excavations  or  with  other  material  such  as 
earth,  gravel,  or  broken  stone.  All  hollows  and  depressions 
which  develop  in  rolling  are  filled  with  suitable  material  and 
the  process  of  filling  and  rolling  is  repeated  until  no  depressions 
develop. 

CLASSIFICATION  OF  MATERIALS.  Different  kinds  of  soils  are 
described  under  the  terms  gravel,  sand,  clay,  marl,  loam,  peat, 
and  muck.  It  is  quite  common  in  grading  specifications  to 
classify  the  materials  to  be  excavated  as  earth,  hardpan,  loose 
rock,  and  solid  rock:  earth  to  include  clay,  sand,  loam,  gravel, 
and  all  hard  material  that  can  be  reasonably  plowed,  and  all 
earthy  matter  or  earth  containing  loose  stones  or  boulders  inter- 
mixed, and  all  other  material  that  does  not  come  under  the 
classification  of  hardpan,  loose  or  solid  rock;  hardpan  to  include 
all  material,  not  loose  or  solid  rock,  that  cannot  be  reasonably 
plowed  on  account  of  its  own  inherent  hardness;  loose  rock 
to  include  all  stone  and  detached  rock,  found  in  separate  masses, 
containing  not  less  than  i  cubic  foot,  nor  more  than  y2  cubic 
yard,  and  all  slate  or  other  rock  soft  or  loose  enough  to  be  re- 
moved without  blasting,  although  blasting  may  occasionally  be 
used;  solid  rock  to  include  all  rock  in  place  and  boulders  measur- 
ing %  cubic  yard  and  over,  in  removing  which  it  is  necessary 
to  resort  to  drilling  and  blasting.  H.  P.  Gillette,  M.  Am.  Soc. 
C.  E.,  subdivides  the  first  class  "earth"  into  three  classifications 
as  (i)  easy  earth,  (2)  average  earth,  (3)  tough  earth.  He  de- 
fines these  classes  as  follows:  "To  the  first  class  belong  loam, 
sand,  and  ordinary  gravel,  which  require  little  or  no  picking  to 
loosen  ready  for  shovelling.  To  the  second  class  belong  sands 
and  gravels  impregnated  with  an  amount  of  clay  or  loam  that 
binds  the  particles  together,  making  it  necessary  to  use  a  pick  or 
plow  drawn  by  two  horses  to  loosen  the  earth  before  shovelling. 
To  the  third  class  belong  the  compact  clays,  the  hardened  crusts 
of  old  roads,  and  all  earths  so  hard  that  one  team  of  horses  can 
pull  a  plow  through  the  earth  only  with  the  greatest  difficulty, 


GRADING,   DRAINAGE,   AND  FOUNDATIONS  97 

0  ' . 

but  that  two  teams  of  horses  on  one  plow  can  loosen  with  com- 
parative ease."  It  is  apparent  that  the  classification  of  mate- 
rials encountered  in  grading  depends  largely  upon  the  judgment 
of  the  engineer.  There  are  very  few  large  grading  contracts  com- 
pleted without  frequent  disputes  arising  between  the  contractor 
and  the  engineer  with  regard  to  classification  of  excavation. 

SHRINKAGE  OF  MATERIALS.  It  is  important  in  grading  opera- 
tions to  distinguish  between  loose  measurement  and  measure- 
ment in  place.  All  estimates  are  generally  based  on  the  yardage 
of  material  in  place.  It  is  a  well-established  fact  that  earth 
when  removed  from  its  original  position  in  a  bank  increases  in 
bulk  or  swells.  It  is  also  well  known  that  when  the  excavated 
material  is  placed  in  a  fill  it  will  shrink  and  settle  so  that  it  will 
occupy  a  smaller  space  than  it  did  originally.  The  swelling  on 
removal  from  the  original  bank  will  vary  generally  from  about 
8  to  15  percent,  but  in  some  cases  may  be  as  high  as  40  to 
50  percent.  The  shrinkage  is  variable  and  depends  upon 
the  kind  of  earth,  the  manner  in  which  the  embankment  is 
made,  and  the  climatic  conditions.  H.  P.  Gillette,  M.  Am. 
Soc.  C.  E.,  states  that  "Clean  sand  and  gravel  swell  14  to  15 
percent;  loam,  loamy  sand  and  gravel  swell  20  percent;  dense 
clay  and  dense  mixtures  of  gravel  and  clay,  33  to  50  percent, 
ordinarily  about  35  percent;  while  unusually  dense  gravel  and 
clay  banks  swell  50  percent."  The  same  authority  says  with 
regard  to  shrinkage,  in  considering  the  different  means  of  com- 
paction, namely,  puddling  action  of  water,  pounding  of  hoofs 
and  wheels,  and  artificial  rolling,  that  "if  the  puddling  action 
of  rains  is  the  only  factor,  a  loose  mass  of  earth  will  shrink 
slowly  back  to  its  original  volume,  but  an  embankment  of  loose 
earth  will  at  the  end  of  a  year  be  still  about  8  percent  greater 
than  the  cut  it  came  from.  If  the  embankment  is  made  with 
small  one-horse  carts  or  wheel  scrapers,  at  the  end  of  the  work 
it  will  occupy  5  to  10  percent  less  space  than  the  cut  from 
which  the  earth  was  taken,  and  in  subsequent  years  will  shrink 
about  2  percent  more,  often  less  than  2  percent.  If  the  em- 
bankment is  made  with  wagons  or  dump-carts  and  made  rapidly 
in  dry  weather  without  water,  it  will  shrink  about  3  to  10  per- 


98  ELEMENTS  OF  HIGHWAY  ENGINEERING 

cent  in  the  year  following  the  completion  of  the  work  and  very 
little  in  subsequent  years.  The  height  of  the  embankment 
appears  to  have  little  effect  on  its  subsequent  shrinkage." 

MACHINES.  Grading  is  accomplished  with  a  variety  of  tools 
and  machines.  A  brief  description  of  the  machines  and  the 
methods  of  operation  will  be  given. 

Carts  and  Wagons.  A  one-horse  tip-cart  is  generally  built 
with  two  wheels.  The  body  tips  over  the  axle  in  discharging 
its  contents.  The  bodies  have  a  capacity  of  about  21  to  24 
cubic  feet,  without  side  boards.  Two-horse  tip-carts  are  operated 
on  the  same  principle,  but  are  built  on  four  wheels.  They  hold 
about  1%  cubic  yards  of  material,  loose  measurement. 

Patent  bottom  dump-wagons  are  made  in  i,  i^,  2,  2^2 ,  and 
3  cubic  yard  sizes.  The  bottom  of  the  wagon  is  made  up  gener- 
ally of  two  leaves,  hinged  either  to  the  sides  or  to  the  ends  of 
the  box.  The  doors  are  held  in  place  with  chains  which  are 
wound  up  on  a  windlass  operated  by  the  driver.  To  dump 
the  load,  the  driver  with  his  foot  kicks  a  release  lever  and  the 
doors  fly  open,  thus  discharging  the  load.  The  doors  are  closed 
by  the  driver  turning  the  windlass.  While  the  body  of  the 
wagon  is  generally  made  of  wood,  the  bottom  doors  are  some- 
times made  of  wood  and  sometimes  of  sheet-iron.  One  of  the 
doors  is  usually  provided  with  a  lip,  which  overlaps  the  joint 
formed  by  the  doors,  and  thus  prevents  the  material  from  sifting 
through. 

Road  Drags.  One  of  the  simplest  and  cheapest  forms  of 
road  drags  is  the  split-log  drag.  A  dry  red-cedar  log  is  best, 
although  red  elm,  walnut,  box  elder,  soft  maple,  and  willow 
make  good  drags.  A  log  should  be  from  7  to  8  feet  in  length 
and  from  10  to  12  inches  in  diameter.  The  log  is  split  as  nearly 
in  half  as  is  practicable,  and  the  heaviest  and  best  slab  is  used 
for  the  front  log.  The  logs  are  braced  together  as  shown  in 
Fig.  31.  An  iron  strip  is  fixed  at  the  ditch  end,  as  shown,  and 
it  projects  %  inch  below  the  lower  edge  of  the  slab  at  its  outer- 
most extremity  and  is  flush  with  the  slab  at  its  other  end.  A 
platform  for  the  driver  is  placed  over  the  cross-braces  on  which 
he  stands.  The  boards  of  the  platform  are  fixed  about  one  inch 


GRADING,   DRAINAGE,   AND   FOUNDATIONS 


99 


apart  to  allow  any  dirt  that  comes  onto  the  platform  to  sift 
through  onto  the  road.  The  chain  is  put  through  the  mid- 
dle of  the  log  at  the  ditch  end  and  passed  over  the  top  of 
the  log  at  its  other  end  and  fastened  to  the  brace.  This  allows 


FIG.  31.     Split-Log  Drag. 


FIG.  32.     Lap-Plank  Drag. 

the  material  to  pass  underneath  the  chain  as  it  runs  from  the 
ditch  along  the  log  to  the  center  of  the  road. 

A  plank-log  drag  is  built  in  a  similar  manner  to  the  split-log 
drag  except  planks  set  on  edge  are  used  in  place  of  the  split 
logs.  The  planks  are  10  to  12  inches  wide  and  2  to  4  inches 


100 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


thick.  A  lap-plank  drag,  shown  in  Fig.  32,  is  used  for  smoothing 
up  a  road  where  only  a  small  amount  of  material  is  to  be  moved. 

Various  forms  of  steel  road  drags  are  manufactured, 
which  have  about  the  same  over-all  dimensions  as  the  split-log 
drag  described  above,  the  logs  or  planks  being  replaced  by  angle 
irons  or  steel  plates  placed  on  edge.  They  weigh  considerably 
more  than  split-log  or  plank  drags,  and  for  this  reason  are  not 
preferred  by  some.  Steel  drags  are  often  equipped  with  a  lever 
by  means  of  which  the  blades  can  be  tilted  at  any  desired  angle. 

Method  of  Operation.     The  team  is  hitched  to  the  chain  so 


FIG.  33- 


Courtesy  of  the  Good  Roads  Machinery  Co. 

Rooter  Plow. 


that  the  drag  will  be  pulled  along  the  road  without  a  load  at 
an  angle  of  about  45  degrees  with  the  center  line,  the  ditch  end 
always  being  ahead.  If  it  is  desired  to  make  the  drag  cut  deeper, 
the  chain  should  be  lengthened,  as  it  is  obvious  that  the  nearer 
the  team  is  to  the  drag,  the  greater  will  be  the  tendency  to  lift  it 
from  the  ground.  The  driver  generally  stands  on  the  drag,  when 
working,  and  by  shifting  his  weight  from  one  end  to  the  other 
causes  the  drag  to  cut  into  the  soil  or  to  drop  the  soil  being  carried 
along  by  it.  To  cut,  he  shifts  his  weight  mostly  on  the  front 
runner  toward  the  ditching  end;  to  cut  light,  he  shifts  his  weight 


GRADING,   DRAINAGE,   AND    FOUNDATIONS: 


toward  the  rear  runner ;  to  drop  the  earth  carried^  along  into 
a  depression,  he  suddenly  shifts  his  weight  to  the  rear  and  to- 
ward the  end  of  the  drag  nearest  the  center  of  the  road. 

Plows.     The    grading    plow  is   so   made    that    the   furrow 
may  be  turned  either  to  the  left  or  to  the  right.     The  function  of 
the  shoe  or  wheel  near  the 
front  end  of  the  beam  is   to 
regulate   the   depth    plowed. 
An    ordinary    grading    plow 
will  make  a  furrow  about  10 
inches  wide  and  from  6  to  12 
inches  deep.    For  breaking  up 
hardpan,    old   macadam,    or 

Other    Stiff    material,     a    rOOter  Courtesy  of  the  Good  Roods' Machinery  Co. 

plow,   as  illustrated    in    Fig.  FIG.  34.    Drag  Scraper. 

33,    is    employed.    A    plow 

of  this  kind  is  generally  pulled  by  a  steam  roller  or  a  trac- 
tor. If  horses  are  used  it  may  require  from  six  to  twelve, 
depending  upon  the  material  plowed. 

Drag  Scrapers.    A  drag  scraper,  as  shown  by  Fig.  34,  con- 
sists of   a  pressed  steel  bowl  to   which   a  bail  and  handles 
are  attached.     They  have  ca- 
pacities of  3,  5,  and  7  cubic 
feet.     These  capacities,  how- 
ever, are  figured  on  the  basis 
of  loose  measurement  and  for 
a  scraper  heaped  full.    This 
form    of    scraper    wears   out 
very   rapidly  on   its   cutting 
edge  and  on  the  bottom,  par- 
ticularly   when    working    in 
hardpan  or  gravel. 
Method  of  Operation.     A  drag  scraper  is  usually  drawn  by 
one  or  two  horses.    To  load,  a  man  grasps  the  handles  and  pushes 
the  cutting  edge  down  into  the  loosened  earth  as  the  scraper 
is  pulled  along.     Then  the  full  scraper  is  dragged  along  on  its 
bottom  to  the  point  of  dump,  where  either  the  driver  or  a  dump- 


Courtesy  of  the  Good  Roads  Machinery  Co. 

FIG.  35.     Wheel  Scraper. 


102  ELEMENTS   OF   HIGHWAY  ENGINEERING 

man  takes  hold  of  one  or  both  of  the  handles  and  lifts  the  scraper 
so  that  it  turns  upside  down  about  its  cutting  edge. 

Wheel  Scrapers.  A  wheel  scraper,  Fig.  35,  is  similar  in 
shape  to  a  drag  scraper,  but  the  bowl  is  fixed  to  two  wheels 
fitted  with  a  pole  and  is  usually  drawn  by  two  horses.  They 
have  capacities  of  9,  12,  and  16  cubic  feet.  Scrapers  with  four 
wheels  are  also  manufactured. 

Method  of  Operation.  A  wheel  scraper  is  operated  as  follows : 
as  it  is  pulled  through  the  plowed  material  in  its  lowered  posi- 
tion, a  man  grasps  the  small  handles  at  the  rear  of  the  bowl  and 
tilts  the  bowl  so  that  the  cutting  edge  engages  with  the  earth. 
When  the  scraper  is  full,  he  pulls  down  on  the  long  lever  at 
the  rear,  which  raises  the  bowl  from  the  ground.  The  lever  is 


Courtesy  of  the  Good  Roads  Machinery  Co. 

FIG.  36.     Four- Wheel  Road  Scraper. 

locked  by  a  catch  and  the  scraper  is  hauled  to  the  dump.  On 
the  small-size  scrapers  no  snatch  team  is  used;  on  the  medium 
size  a  snatch  team  is  generally  used;  and  on  the  large  size  a 
snatch  team  is  always  used.  A  snatch  team  consists  of  a  pair 
of  horses,  which  is  hitched  to  the  pole  in  front  of  the  team 
dragging  the  scraper  during  the  process  of  loading. 

Road  Scrapers  or  Graders.     There  are  several  different  types 
of  road  scrapers  or  road  hones.    The  four-wheel  machines,  Fig. 


GRADING,   DRAINAGE,   AND   FOUNDATIONS  103 

36,  have  blades  from  7  to  8  feet  long,  made  up  pf  two  parts, 
a  cutting  edge  and  a  mold  board.  The  blade  is  suspended  from 
a  part  of  a  full  circular  frame  attached  to  the  machine.  By 
turning  the  large  wheels  the  blades  may  be  tilted  at  any  desired 
angle  with  the  vertical.  It  is  also  possible  to  turn  the  blade 
through  any  desired  horizontal  angle.  In  some  types  of  machines 
the  blade  is  given  a  forward  or  backward  tilt  by  attachments 
fixed  directly  to  the  blade,  while  in  others  the  blade  is  fixed  in 
this  respect,  and  the  tilt  is  obtained  by  lowering  or  raising  the 
front  end  of  the  frame  over  the  front  axle.  It  is  also  possible 
in  some  types  to  shift  the  blade  sideways  so  as  to  project  be- 
yond the  wheels  for  some  distance,  which  is  a  great  convenience 
in  filling  in  ditches  or  cutting  down  banks.  The  framework  is 
generally  made  of  steel  shapes,  although  wood  is  sometimes  used. 
Another  feature  of  many  of  the  four-wheel  machines  is  that  the 
rear  axle  is  made  telescopic  so  that  either  wheel  may  be  shifted 
in  a  lateral  direction.  This  adjustment  enables  the  rear  wheels 
to  straddle  a  furrow  or  to  engage  with  the  side  of  the  banks 
and  thus  prevent  side  slip.  In  some  makes  the  rear  axle  is 
pivoted  so  that  it  will  turn  through  a  small  horizontal  angle, 
helping  the  machine  to  keep  in  place  when  in  the  center  of  the 
road.  There  are  some  types  also  in  which  the  rear  wheels  are 
so  fixed  to  the  axle  that  they  may  always  be  made  perpendicular 
to  the  slope  on  which  the  machine  is  travelling.  All  of  these 
different  adjustments  are  carried  out  by  one  man,  who  stands 
on  the  rear  of  the  machine  and  operates  the  various  wheels  and 
levers,  all  of  which  are  within  easy  reach.  Various  types  of 
two-wheel  scrapers  are  also  manufactured. 

Method  of  Operation.  In  grading  by  means  of  a  scraper  the 
dry  grass  and  sod  is  first  burnt  off.  A  cut  is  then  made  at  the 
edge  of  the  ditch,  using  the  point  of  the  blade,  the  latter  being 
set  at  a  sharp  angle  so  that  only  the  point  and  a  very  short 
length  of  the  blade  come  in  contact  with  the  ground.  On  the 
next  round  the  blade  is  lowered  to  a  flatter  angle  and  the  earth 
is  moved  along  the  blade  toward  the  center  of  the  road.  By 
making  several  rounds  of  the  scraper  in  this  manner  the  road- 
bed is  crowned  up  at  the  center.  To  smooth  out  the  roadbed, 


104  ELEMENTS  OF  HIGHWAY  ENGINEERING 

the  surface  is  first  thoroughly  harrowed  to  break  up  the  large 
lumps,  and  then  the  scraper  is  drawn  along  the  road  with  the 
blade  set  at  right  angles  to  the  center  line  of  the  road.  When  a 
reversible  machine  is  used  the  blade  is  turned  around  so  that 
the  convex  side  is  ahead.  A  plow  is  not  necessary  in  scraper 
work,  since  the  machine  can  generally  do  all  the  plowing  de- 
sired with  the  point  of  the  blade.  In  order  not  to  get  a  soft 
road  it  is  not  advisable  to  move  the  earth  up  with  the  scraper 
in  layers  over  4  inches  deep.  In  some  cases  from  one  to  three 
furrows  are  plowed  at  the  ditch  side  of  the  road,  the  material 
being  turned  toward  the  center.  The  scraper  is  then  set  to 
work  at  the  furrow  nearest  the  center,  and  it  moves  over  from 
this  furrow  toward  the  center  only  about  as  much  earth  as  is 
loosened  by  the  first  round  of  the  scraper.  The  next  furrow  is 
moved  over  in  a  similar  manner,  and  the  process  is  repeated 
until  the  tast  furrow  is  reached,  which  is  moved  over  in  turn. 
The  road  is  then  smoothed  out.  The  four-wheel  machines  for 
heavy  work  require  from  four  to  six  horses,  whereas  two  horses 
are  used  when  the  work  is  light.  On  the  lighter  two-wheel 
machines  from  two  to  four  horses  are  necessary,  depending  upon 
the  character  of  the  work. 

Elevating  Graders.  The  principal  parts  of  the  elevating 
grader,  shown  in  Fig.  37,  are  the  plow  and  mold  board  and  the 
elevating  belt.  A  disk  plow  is  sometimes  substituted  for  the 
pointed  plow.  The  mold  board  back  of  the  plow  is  shaped 
so  as  to  deliver  the  furrow  to  the  elevating  belt  with  as  little 
loss  as  possible.  The  elevating  belt  carriers  are  made  in  3-  to 
5-foot  sections,  so  that  any  length  from  15  to  30  feet  can  be 
obtained  ir;  some  of  the  larger  machines.  The  carrier  is  run 
either  with  gears  driven  by  the  wheels  or  by  a  gasoline  engine 
set  on  the  rear  of  the  grader.  When  the  carrier  is  driven  by  an 
engine  it  requires  less  power  to  haul  the  machine. 

Method  of  Operation.  For  heavy  work  the  grader  requires 
twelve  horses,  eight  being  hitched  in  front  and  four  in  the  rear, 
two  drivers  and  two  operators  on  the  machine,  who  operate  the 
various  levers  controlling  the  movements  of  the  plow  and  belt. 
A  25-horse-power  traction  engine  may  be  used  in  place  of  the 


Courtesy  of  ihe  A  usttn  Manufactut  ins  Co. 


FIG.  37.     Elevating  Grader. 


FIG.  38.     Steam  Shovel  Used  on  Heavy  Highway  Grading  Work. 


106  ELEMENTS   OF  HIGHWAY   ENGINEERING 

horses.  The  grader,  as  it  moves  along,  plows  up  the  earth, 
which  is  thrown  onto  the  elevating  belt  and  discharged  over 
its  end,  either  onto  the  road  or  into  wagons. 

Steam  Shovels.  On  heavy  grading  operations  steam  shovels 
of  the  type  shown  in  Fig.  38  are  economically  employed. 

Horse  Rollers.  A  horse  roller  is  generally  made  with  one 
large  roller  having  a  face  of  about  5  feet  and  a  diameter 
of  about  5  feet.  Any  weight  desired  from  1^/2  to  $y2  tons, 
varying  by  i  ton,  can  be  obtained.  Additional  weight  may  be 
placed  in  the  boxes  at  either  end  of  the  frame  and  the  weight 


Courtesy  of  the  Good  Roads  Machinery  Co. 

FIG.  39.     Horse  Roller. 

be  thus  increased  by  i  ton.  The  roller  is  made  of  steel  or  cast 
iron.  An  essential  feature  of  a  horse-drawn  roller  is  to  have 
it  reversible,  so  that  it  can  be  drawn  in  either  direction.  In 
Fig.  39  the  two- wheel  truck  may  be  uncoupled  and  attached 
to  the  opposite  end  of  the  roller.  A  grooved  roller  is  some- 
times specified,  due  to  the  fact  that  better  compression  can  be 
obtained  than  with  the  smooth-faced  roller.  The  grooves  are 
formed  by  bars  bolted  around  the  face  of  the  roller  parallel  to 
the  edges  and  at  a  small  interval  apart. 


GRADING,   DRAINAGE,   AND   FOUNDATIONS  109 

Three- Wheel  Rollers.  Three-wheel  rollers  vary  in  weight 
from  10  to  20  tons.  The  majority  of  rollers  of  this  type  are  run 
by  steam,  although  there  are  a  few  makes  which  are  run  by 
gasoline  engines.  Fig.  40  shows  a  three-wheel  steam  roller, 
and  Fig.  41  a  three- wheel  roller  operated  by  gasoline  engine. 
Rollers  are  generally  furnished  with  a  high  and  low  speed.  The 
low  speed  is  used  in  rolling  embankment,  subgrade,  telford,  etc., 
while  the  high  speed  is  used  in  finishing  the  surface  or  in  travelling 
from  point  to  point. 

Tandem  Rollers.  The  weight  of  tandem  rollers  varies  from 
3  to  12  tons.  These  rollers  are  commonly  run  by  steam,  see 


Courtesy  of  the  Buffalo  Steam  Roller  Co. 

FIG.  42.     Tandem  Steam  Roller. 

Fig.  42,  although  there  are  some  makes,    see   Fig.    43,    which 
are  run  by  gasoline  engines. 

Scarifiers.  This  machine  consists  of  a  heavy  cast-iron  block 
on  two  or  four  wheels  which  holds  a  series  of  steel  picks.  The 
block  weighs  about  three  tons  and  the  picks  can  be  adjusted 
in  the  block  or  the  block  itself  arranged  so  that  any  depth 
desired  up  to  5  or  6  inches  can  be  picked  up.  The  picks  are 
arranged  in  either  a  straight  line  or  in  two  lines  which,  together, 
form  a  V.  Most  of  the  scarifiers  are  so  designed  that  it  is  not 


GRADING,   DRAINAGE,   AND   FOUNDATIONS 


111 


necessary  to  turn  them  around.  This  is  accomplished  generally 
by  having  two  sets  of  picks,  one  set  being  used  when  the  ma- 
chine runs  in  one  direction  and  the  other  when  in  the  opposite 
direction.  Scarifiers  of  this  type  are  towed  by  a  chain  hitched 
to  the  roller.  The  arrangement  of  the  picks  and  the  form  of  the 


Courtesy  of  Charles  Hvass  and  Co, 

FlG.  44.     Hvass  Scarifier. 

blocks  vary,  but  all  of  the  machines  work  on  the  same  princi- 
ple. Figs.  40  and  44  show  two  American  scarifiers  which  are 
typical  of  the  block  type. 

Watering  Carts.  •  In  the  United  States  the  cart  used  for 
sprinkling  generally  consists  of  a  cylindrical  tank  mounted  hori- 
zontally on  a  four-wheel  truck.  The  tank  may  be  made  either 
of  wood  or  of  steel.  The  capacities  vary  from  350  to  1,000 
gallons.  Carts  with  horizontal  valves  throw  the  water  out  in 
horizontal  sheets,  while  those  with  vertical  valves  distribute  the 
water  in  vertical  sheets.  (See  Fig.  45.) 

DRAINAGE 

OBJECT  OF  DRAINAGE.  In  the  construction  of  any  type  of 
road  or  street,  drainage  is  of  the  utmost  importance,  as  water 


••'• 


112 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


in  the  subgrade  or  on  the  surface  is  one  of  the  most  destructive 
agents  encountered  in  the  maintenance  of  highways.  Provisions 
for  drainage  should  be  made  so  that  water  will  neither  be  re- 
tained in  the  substructure  beneath  the  roadway  nor  stand  on 
the  surface  nor  at  the  sides  of  the  roadway.  Since  the  loads  which 
come  on  a  roadway  surface  must  ultimately  be  borne  by  the 
natural  soil,  it  is  obvious  that  a  dry  condition  of  the  subsoil  is 
a  prerequisite  for  the  proper  accomplishment  of  this  duty. 


Courtesy  of  the  Austin  M/R.  Co. 


FIG.  45.     Watering  Carts. 


A  soil  which  is  saturated  with  water  will  have  a  very  low  sup- 
porting power.  Drainage  may  be  properly  considered  under 
two  main  heads,  subdrainage  and  surface  drainage. 

SUBDRAINAGE.  Conditions  Encountered.  Geological  struc- 
ture, the  location  of  the  highway,  and  the  climatic  conditions  are 
important  factors  in  subdrainage  design.  If  the  subsoil  of  a  high- 
way is  of  a  sandy  or  gravelly  nature  and  the  highway  is  located 
on  high  ground  so  that  the  water  as  it  seeps  through  the  soil 
readily  runs  off,  subdrainage  is  not  necessary.  On  the  other 


GRADING,   DRAINAGE,   AND   FOUNDATIONS  113 

hand,  a  roadway  surface  of  a  clayey  or  other  plastig  soil,  which 
readily  retains  water,  will  become  almost  impassable  unless 
properly  subdrained.  Springs,  which  occur  on  hillsides,  unless 
led  from  the  highway  by  subdrains,  will  soften  the  subsoil.  A 
stratum  of  rock  may  lie  near  the  surface  and  water  may  col- 
lect in  its  depressions  and  tend  to  soften  the  overlying  road. 

If  water  is  allowed  to  remain  in  the  subsoil  in  cold  weather, 
the  ground  freezes  and  expands,  thus  loosening  the  soil.  It  is 
quite  essential,  when  the  frost  comes  out  of  the  ground  in  the 
spring,  to  provide  means  so  that  the  water  below  the  surface, 
which  has  accumulated  by  thawing,  will  be  immediately  carried 
away.  Since  the  thawing  action  takes  place  below  as  well  as 
near  the  surface,  the  foundation  will  soon  soften  if  the  resultant 
water  is  not  removed.  Subdrains  properly  placed  will  remove 
this  water.  The  hydrostatic  pressure  of  water  in  places  higher 
than  the  level  of  the  highway  may  force  the  water  slowly  up 
through  the  soil,  which  fact  may  explain  the  presence  of  water 
in  a  road  during  a  thaw  where  it  was  known  that  the  ground 
when  frozen  was  comparatively  dry. 

Pipe  Drains.  One  of  the  best  and  cheapest  methods  of  ac- 
complishing subdrainage  is  by  means  of  lines  of  tile  pipe. 

The  Pipe.  The  pipe  may  be  made  of  either  cement  or 
vitrified  clay.  The  cement  pipes  are  generally  made  with  plain 
ends  and  the  vitrified  pipes  with  bell  and  spigot  ends.  The 
pipes  are  made  in  i-foot  lengths  for  small  diameters  and  in 
2-foot  lengths  for  large  diameters. 

Determination  of  Size  of  Pipe.  The  requisite  size  of  pipe 
required  depends  upon  the  amount  of  water  to  be  carried  and 
the  grade  to  which  the  pipe  is  laid.  There  are  several  formulas 
by  means  of  which  the  size  can  be  determined.  The  assumptions 
that  must  be  made,  however,  in  applying  a  formula  to  any  par- 
ticular case  are  such  as  to  render  an  accurate  determination  of 
the  proper  size  impossible.  For  instance,  the  amount  of  water 
to  be  carried  off  cannot  be  more  than  roughly  approximated, 
and  very  little  reliable  data  relative  to  the  flow  of  water  in 
pipes  of  this  kind  are  obtainable.  The  amount  of  water  is  gener- 
ally assumed  to  vary  between  y£  inch  and  i  inch  per  acre  per 


114  ELEMENTS   OF  HIGHWAY  ENGINEERING 

twenty-four  hours  on  the  area  to  be  drained,  an  average  value 
being  ^  inch.  Experience  as  to  what  a  tile  drain  has  accom- 
plished in  any  particular  locality  is  a  better  guide  than  any 
result  that  may  be  obtained  by  formula.  It  has  been  well  estab- 
lished in  practice  that  the  minimum  size  should  be  4  or  5  inches. 
In  places  where  no  drains  have  been  laid,  the  size  of  pipe  ob- 
tained by  formulas  may  serve  as  a  guide  in  judging  of  the  proper 
size  to  be  used.  The  following  formula  is  given  by  Professor 
I.  O.  Baker,  M.  Am.  Soc.  C.  E.: 


A  I  W 

A  =  i.9>|  j- 


in  which  A  is  the  number  of  acres  for  which  a  tile  having  a 
diameter  of  d  inches  and  a  fall  of  /  feet  in  a  length  of  L  feet 
will  remove  i  inch  of  water  in  twenty-four  hours. 

Laying  the  Pipe.  The  pipe  is  usually  laid  at  the  sides  of 
the  road  along  the  lines  of  the  open  ditches  and  at  a  depth  of 
2^  to  3  feet  below  the  bottom  of  the  ditch.  The  necessity  for 
a  line  of  pipe  at  each  side  of  the  road  is  wholly  a  matter  of 
judgment.  Generally  on  side  hills  where  a  subdrain  is  needed, 
a  single  line  on  the  uphill  side  of  the  road  will  serve  to  cut  off 
the  water  coming  through  the  soil.  On  hills  the  pipe  may  be 
laid  under  the  shoulders  of  the  road,  since,  if  placed  in  the  ditch, 
it  is  liable  to  be  washed  out.  On  streets  that  are  paved  and 
curbed  the  pipe  is  frequently  laid  underneath  the  curbs.  An- 
other method  of  constructing  pipe  drams  is  to  lay  lines  of  pipe 
at  intervals,  either  transversely  or  in  the  form  of  a  V,  the  ends 
of  the  pipes  opening  into  the  side  ditches.  After  the  pipe  is 
laid  the  trench  is  filled  with  broken  stone,  gravel,  earth,  brush, 
or  a  combination  of  these  materials.  The  drains  constructed  by 
the  Massachusetts  and  Maryland  Highway  Commissions  are  laid 
as  follows:  2  inches  of  broken  stone  or  gravel  which  will  pass 
through  a  ij^-inch  mesh  and  not  through  a  ^-inch  mesh  is 
used  for  a  bed;  the  joints  are  left  open;  clean  gravel  or  broken 
stone  of  the  sizes  already  described  is  filled  about  the  pipe  and 
over  it  for  a  depth  of  i  foot;  the  remainder  of  the  trench  is 
filled  with  stone  which  will  pass  through  a  3-inch  and  not  through 


GRADING,   DRAINAGE,   AND   FOUNDATIONS  115 

a  i-inch  screen.     (See  Fig.  46.)     All  drains  must  be  carried  to  a 

proper  outlet,  such  as  a  culvert,  ditch,  or  another  drain.    The 

minimum  grade  of  pipe   is   specified   by  some   engineers   as  6 

inches  in  100  feet,  whereas  others  will  allow  as  small  a  fall  as 

%  inch  in  100  feet.    In  clayey  soils  a  tile  pipe 

will  drain  a  width  about  six   times  its  depth 

on  each  side;    in  porous  soils  the    distance 

drained  on  each  side  may  be  as   much    as 

fifteen  or  twenty  times  its  depth  below  the 

surface. 

Cost  of  Pipe  Drains.    Pipe  drains  are  gen- 
erally paid  for  at  a  price  per  linear  foot,  which 
includes  the  cost  of  trenching,   refilling  with  FIG.  46.  Pipe  Drain, 
gravel  or  broken  stone,  the  cost  of  pipe  and 
laying.     Fifty  cents  is  an  average  price  per  foot  for  pipe  drains 
used  on  state  highway  work. 

Blind  and  Other  Drains.  Blind  drains  are  generally  con- 
structed by  excavating  a  trench  from  i  to  2  feet  in  width.  The 
trench  is  partially  filled  with  broken  stone,  gravel,  or  other  porous 
material.  Such  drains  may  be  constructed  alongside  or  across 
the  road  at  intervals.  They  serve  the  same  purpose  as  a  tile 
pipe,  but  they  are  not  as  effective  as  pipe  drains,  as  they  are 
more  liable  to  clog  up.  The  drainage  of  some  soils  can  be  im- 
proved by  excavating  and  refilling  with  a  porous  material.  Gen- 
erally, however,  the  depth  at  which  the  road  must  be  subdrained 
is  such  that  to  accomplish  effective  results  by  this  method  makes 
the  cost  excessive. 

SURFACE  DRAINAGE.  Side  Ditches  and  Gutters.  The  trans- 
verse slopes  or  crown  of  the  roadway  serve  to  remove  the  water 
from  the  surface  to  the  ditches  or  gutters  at  the  side,  whence 
it  follows  the  longitudinal  grade  to  the  point  of  outlet  which 
may  be  a  culvert,  natural  waterway,  or  catch-basin.  The 
amount  of  crown  of  different  types  of  roads  and  pavements, 
methods  of  obtaining  same,  and  the  minimum  longitudinal  grade 
have  been  previously  discussed  in  Chapter  IV. 

On  roads  it  is  usually  necessary  to  construct  ditches  only  in 
cuts,  since  on  fills  the  grade  of  the  roadway  is  raised  above  the 


116 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


general  ground  level.  When  the  fills  are  shallow  or  the  road 
has  a  steep  grade,  the  construction  of  gutters  may  be  advisable 
to  protect  the  shoulder  of  the  road.  The  ditch  or  gutter  usually 
has  the  same  grade  as  that  of  the  center  of  the  road,  although 
on  very  flat  grades  the  ditch  may  have  a  steeper  grade  than  the 


6"to  <J" 

FIG.  47.     V-shaped  Ditch. 


-18- 


FiG.  48.     Wide  and  Flat  Ditch. 


FIG.  49.     Ditch  with  Trapezoidal  Section. 

roadway.  The  cross-section  of  the  ditch  is  usually  made  in 
one  of  the  following  forms:  the  V-shaped,  the  trapezoidal,  or  the 
wide  flat  ditch.  The  last  type  is,  in  reality,  formed  by  a  continua- 
tion of  the  slope  of  the  roadway  surface.  A  ditch  having  a 
trapezoidal  or  a  V-shaped  cross-section  will  carry  more  water, 
but  is  very  much  more  liable  to  gully  out  than  one  constructed 
wide  and  flat.  Other  advantages  of  the  wide  and  flat  ditch  are 
that  it  is  not  so  dangerous  for  the  traffic  and  that  it  is  much  easier 
to  construct  and  maintain,  particularly  if  a  road  grader  is  used 
in  accomplishing  the  work.  The  width  and  depth  of  the  ditch 
depend  upon  the  amount  of  water  to  be  carried,  and  vary  to 
some  extent  with  the  width  of  the  road.  Typical  sections  of 
ditches  are  shown  in  Figs.  47,  48,  and  49. 

Water  should  not  be  carried  too  great  a  distance  in  a  ditch 
before  it  is  given  an  outlet,  since  the  amount  of  water  will  be- 
come so  great  that  the  capacity  of  the  ditch  will  be  exceeded, 
and  gullying  will  result.  It  is  also  easier  to  turn  off  a  small 


GRADING,   DRAINAGE,  AND  FOUNDATIONS  117 

amount  of  water  into  the  adjacent  fields  without  objection  on 
the  part  of  the  property  owner,  than  it  is  to  dispose  of  a  large 
amount  in  this  manner.  There  are  places  along  the  road  where 
the  water  may  be  turned  off  at  each  side,  such  places,  for  in- 
stance, as  fills  with  the  ground  sloping  away  from  the  road 
on  both  sides.  If  there  is  much  water  to  be  turned  over  a  bank 
in  this  manner  it  will  be  necessary  to  protect  the  bank  from 
washing  out.  A  small  amount  of  water  running  down  high 
banks  composed  of  sandy  soil  is  liable  to  cause  great  damage, 
for  the  small  gullies  made  by  the  water  may  rapidly  extend 
back  into  the  roadway  surface.  The  bank  should  be  protected 
by  sod,  or  a  paved  gutter  should  be  built  down  the  side  of  the 
bank  to  carry  the  water.  On  hills  where  the  grade  exceeds  3 
percent  and  the  soil  is  loose  and  sandy,  it  may  be  necessary 
to  pave  the  ditch  with  cobble-stone,  field-stone,  brick,  or  paving 
blocks  in  order  to  prevent  gullying.  The  construction  of  gutters 
used  in  connection  with  various  pavements  is  considered  in 
detail  in  Chapter  XX. 

FOUNDATIONS 

NECESSITY  OF  FOUNDATIONS.  The  soil  composing  the  sub- 
grade,  which  will  be  designated  the  natural  foundation,  eventually 
supports  the  weight  of  traffic  on  the  wearing  course  of  the  road- 
way. Usually  the  soil  does  not  possess  sufficient  bearing  power 
to  support  adequately  the  wearing  course  and  the  traffic  "which 
comes  upon  it.  It  is  necessary,  therefore,  to  utilize  an  artificial 
foundation,  which  has  been  defined  as  "that  layer  of  the  founda- 
tion especially  placed  on  the  subgrade  for  the  purpose  of  rein- 
forcing the  supporting  power  of  the  latter  itself,  and  composed 
of  material  different  from  that  of  the  subgrade  proper."*  Thus 
traffic  loads  are,  under  average  conditions,  transmitted  through 
the  wearing  course  of  the  roadway  to  the  artificial  foundation, 
and  thence  to  the  natural  foundation  or  the  subgrade  of  the 
highway.  It  is  thus  seen  that  as  the  traffic  loads  increase  with 
a  given  kind  of  soil  or  as  the  supporting  power  of  the  natural 

*  1914  Proceedings,  Am.  Soc.  C.  E.,  page  3015. 


118  ELEMENTS   OF  HIGHWAY  ENGINEERING 

foundation  decreases,  the  strength  or  thickness  of  the  artificial 
foundation  must  be  increased. 

The  subject  of  foundations  will  be  considered  under  two 
main  heads,  namely,  natural  foundations  and  artificial  founda- 
tions. With  the  exception  of  earth  and  sand-clay  roads,  the 
construction  of  all  of  the  more  common  types  of  roads  and 
pavements  might  be  described  as  composed  of  three  distinct 
steps:  the  construction  of  the  subgrade  or  natural  foundation, 
the  construction  of  an  artificial  foundation,  and  the  construc- 
tion of  the  wearing  course  or  pavement.  On  this  assumption, 
therefore,  the  lower  courses  of  either  a  broken  stone  or  a  gravel 
road  will  be  considered  as  types  of  artificial  foundations. 

NATURAL  FOUNDATIONS.  The  natural  foundation  is  com- 
posed of  rock,  gravel,  or  some  kind  of  soil.  The  different  types 
of  rock  are  considered  in  Chapter  VIII  and  the  characteristics 
and  occurrence  of  gravel  in  Chapter  VII. 

Soil  Classification.  Soil  is  defined  as  "a  mixture  of  fine 
earthy  material  with  more  or  less  organic  matter  resulting  from 
the  growth  and  decomposition  of  vegetation  or  animal  matter."* 
The  majority  of  soils  are  of  mineral  origin  and  are  formed  by 
the  breaking  down  of  rocks  through  the  agency  of  the  wind, 
water,  and  glaciers  in  combination  with  temperature  changes, 
chemical  action,  and  plant  growth.  Soils  may  be  designated  as 
sedentary  or  transported.  Sedentary  soils  are  those  which  re- 
main near  their  source  of  formation.  Transported  soils,  as  the 
name  implies,  have  been  carried  by  some  geological  agency, 
generally  either  rivers  or  glaciers,  from  the  place  where  they 
were  first  formed  to  some  other  locality.  Generally  the  prin- 
cipal constituents  of  soil  are  silica,  with  varying  amounts  of 
alumina,  oxides  of  iron,  lime,  magnesia,  and  the  alkalies,  to- 
gether with  a  small  amount  of  organic  matter.  The  common 
soils  encountered  in  highway  work  are  classified  as  sand,  clay, 
loam,  marl,  peat,  and  muck. 

Sand.  Sand  has  been  defined  as  "finely  divided  rock  detritus 
the  particles  of  which  will  pass  a  lo-mesh  and  be  retained  on 
a  2oo-mesh  sieve."* 

*  Proposed  by  Committee  D-4,  Am.  Soc.  Testing  Materials. 


GRADING,   DRAINAGE,   AND   FOUNDATIONS  119 

Clay.  Clay  is  "finely  divided  earth,  generally  eilicious  and 
aluminous,  which  will  pass  a  2oo-mesh  sieve."*  Clays  result 
mainly  from  the  decomposition  of  feldspar  and  micaceous  rocks. 
When  wet  a  clay  becomes  very  plastic  and  is  extremely  unstable, 
and,  due  to  its  impermeable  qualities,  it  dries  out  slowly.  A 
clay  becomes  hard  in  drying  and  contracts  to  such  an  extent 
that  areas,  where  large  clay  deposits  occur,  are  traversed  by 
wide  cracks. 

Shale.  Shales  are  chemically  of  the  same  composition  as 
clays.  They  have  a  laminated  structure  and  are  similar  in 
appearance  to  slates.  Shales  will  rapidly  disintegrate  on  exposure 
to  the  atmosphere. 

Loam.  Loam  is  "finely  divided  earthy  material  containing 
a  considerable  proportion  of  organic  matter."!  Loams  may  be 
any  soil  between  sand  and  clay,  as  they  contain  more  or  less  of 
each  of  these  materials.  They  may  be  classified  as  heavy 
clay  loams,  clay  loams,  sandy  loams,  and  light  sandy  loams, 
depending  upon  the  quality  of  the  sand  or  clay  content.  Stock- 
bridge  classifies  loams  as  follows:  "Heavy  clay  loam  with  10  to 
25  percent  of  sand;  clay  loam  with  25  to  40  percent  of  sand; 
loam  with  40  to  60  percent  of  sand;  sandy  loam  with  60  to 
75  percent  of.  sand;  light  sandy  loam  with  75  to  90  percent 
of  sand."  In  the  Middle  West  a  black  loam  which  contains  so 
much  clay  as  to  be  sticky  when  wet  is  known  as  "gumbo." 

Marl.  Marl  is  a  term  which  is  applied  to  all  calcareous 
clays  containing  a  minimum  of  15  percent  of  carbonate  of  lime 
and  a  maximum  of  75  percent  of  clay.  The  larger  the  propor- 
tion of  carbonate  of  lime,  the  less  plastic  is  the  material  until 
finally  it  is  no  longer  considered  as  marl,  but  is  called  argillaceous 
limestone. 

Peat  and  Muck.  Peat  and  muck  are  generally  distinguished 
from  other  soils  by  the  presence  of  humus  or  vegetable  matter. 
Peat  is  formed  by  the  decomposition  of  vegetable  matter  under 
water.  Humus  is  the  soil  resulting  from  the  decomposition  of 
vegetable  matter  on  the  surface  of  the  ground. 

*  1914  Proceedings,  Am.  Soc.  C.  E.,  pages  3013  and  3017. 
t  1914  Proceedings,  Am.  Soc.  C.  E.,  page  3015. 


120  ELEMENTS   OF   HIGHWAY  ENGINEERING 

Loads  on  the  Foundation.  The  safe  loads  per  square  foot 
specified  by  Professor  William  H.  Burr,  M.  Am.  Soc.  C.  E.,  for 
foundations  are  as  follows: 

Well-drained  clay  practically  dry 8,000  to  12,000  pounds 

Clay  moderately  dry 4,000  to    8,000  " 

Soft,  moist  clay 2,000  to    4,000  " 

Coarse  sand  or  gravel  in  undisturbed  and  well-bonded 

strata 12,000  to  18,000  " 

Thoroughly  compacted  and   bonded   ordinary  sand 

well  held  in  place 4,000  to    8,000  " 

It  is  generally  assumed  that  the  lines  of  pressure  of  a  load 
which  is  supported  on  an  appreciable  depth  of  earth,  concrete, 
stone,  or  other  stable  material,  will  diverge  from  the  point  of 
contact  in  all  directions  at  an  angle  of  about  45  degrees. 

Improving  the  Natural  Foundation.  Gravel,  clay,  and  sand 
make  excellent  foundations  if  well  drained.  A  clayey  subsoil 
may  be  improved  by  the  addition  of  sand  or  gravel,  while  a 
sandy  subsoil  may  be  improved  and  made  more  unyielding  by 
the  addition  of  clay.  Muck  should  be  removed  for  a  certain 
depth,  varying  with  local  conditions,  and  replaced  with  some 
other  material.  The  availability  of  materials  will  usually 
determine  which  of  the  following  should  be  used  for  adding 
to  or  replacing  the  unsatisfactory  soil:  broken  stone,  stone 
screenings,  gravel,  sand,  shells,  cinders,  clinkers,  brickbats, 
slag,  or  clay.  Any  subsoil  will  generally  be  improved  by  rolling, 
and  such  a  process  will  show  up  weak  spots,  which  should  be  re- 
placed with  other  material. 

ARTIFICIAL  FOUNDATIONS.  This  class  of  foundations  is  usu- 
ally constructed  of  large  stone,  gravel,  broken  stone,  slag,  hy- 
draulic cement-concrete,  or  bituminous  concrete.  Brush  and 
plank  have  been  employed  in  the  construction  of  foundations 
through  swampy  land.  Old  pavements  have  frequently  been 
made  to  serve  as  foundations  for  surfaces  of  some  other  type. 
The  selection  of  any  particular  type  is  governed  principally  by 
considerations  of  the  type  of  roadway  surface  to  be  supported, 
the  traffic  to  which  the  surface  is  subjected,  relative  cost  of 
available  materials,  and  the  natural  soil  conditions. 

Stone  Foundations.     In  this  class  are  included,  besides  the 


GRADING,   DRAINAGE,  AND   FOUNDATIONS  121 

methods  originally  proposed  by  Telford  and  Tresaguet,  V-drain 
foundations  and  foundations  composed  of  broken  stone  or  similar 
material. 

Telford  Foundation.  Telford,  in  constructing  broken  stone 
roads,  advocated  the  use  of  a  foundation  of  large-size  stone 
carefully  placed  by  hand.  His  method  followed  that  previously 
adopted  by  Tresaguet,  the  principal  difference  between  the  two 
methods  being  that  Telford  placed  his  foundation  on  a  flat 
subgrade  and  obtained  the  crown  in  the  foundation  by  using 
stones  of  different  depths  from  the  center  to  the  sides,  whereas 
in  Tresaguet's  method  a  subgrade  parallel  to  the  finished  sur- 
face was  employed  and  all  the  stones  were  practically  of  the 
same  depth.  Foundations  constructed  by  both  methods  are 
now  called  Telford. 

There  are  conditions  under  which  a  Telford  foundation  will 
give  results  that  are  economical,  but  its  universal  use  should 
not  be  recommended,  since  experience  has  demonstrated  that  a 
broken  stone  road  without  such  a  foundation  on  a  well-drained 
and  compacted  subsoil  is  fully  capable  of  carrying  a  considerable 
traffic.  Telford  is  advisedly  used  on  wet  soils  where  small  broken 
stone  would  be  pushed  down  into  the  soft  soil. 

A  Telford  foundation  is  usually  constructed  on  a  subgrade, 
the  surface  of  which  is  parallel  to  the  finished  surface  of  the 
road.  The  stones  used  vary  from  3  to  8  inches  in  width,  6  to 
15  inches  in  length,  and  from  6  to  8  inches  in  depth.  The  stones 
are  carefully  laid  on  the  subgrade  with  the  greatest  length  across 
the  road,  and  the  widest  edge  down.  The  projecting  edges  of 
the  stones  above  the  surface  are  knocked  off  with  a  hammer, 
and  the  spaces  between  the  stones  are  packed  and  wedged  with 
spalls.  The  whole  surface  is  then  rolled  with  a  heavy  roller. 
It  is  then  ready  to  receive  the  upper  courses  of  stone.  The 
cost  of  Telford  foundations  varies  from  35  cents  to  about  $i 
per  square  yard.  The  thickness  of  the  course  and  the  availability 
of  the  material  largely  affect  the  cost  of  this  type  of  foundation. 

V -Drain  Foundation.  A  V-drain  foundation  is  constructed 
by  excavating  the  roadway  for  its  full  width,  from  4  to  8  inches 
deep  at  the  sides  and  from  12  to  18  inches  deep  at  the  center, 


122  ELEMENTS   OF  HIGHWAY  ENGINEERING 

thus  producing  a  flattened  " V-shaped"  trench.  This  type  of 
construction  serves  as  a  drain  as  well  as  a  foundation.  The 
excavated  space  is  filled  with  boulders  and  small  stone,  as  is 
shown  in  Fig.  50.  The  larger  stones  are  placed  at  the  bottom 
of  the  trench  and  the  smaller  stones  at  the  top.  The  trench  is 


FIG.  50.     V-Drain. 

intercepted  by  culverts,  constructed  across  the  road  at  the  low 
points,  which  take  away  the  water  that  flows  through  the  V-drain. 
The  price  of  V-drain  is  sometimes  stated  as  so  much  a  linear 
foot,  which  method  is  rather  indefinite  unless  the  cross-section 
of  drain  is  known.  Contract  prices  vary  from  75  cents  to  $1.25 
per  cubic  yard. 

Broken  Stone  Foundation.  The  lower  or  bottom  course  of 
a  broken  stone  road,  when  the  latter  is  built  in  two  courses,  is 
the  foundation  for  the  upper  or  wearing  course.  In  the  United 
States  this  course  is  usually  about  4  inches  in  depth  after 
compaction,  but  should  be  as  much  as  6  to  8  inches  in  order 
to  take  the  increased  loads  due  to  modern  traffic.  Where  the  sub- 
soil is  poor  or  the  road  is  subjected  to  very  heavy  traffic,  or  where 
it  is  desired  to  aid  the  subdrainage  of  the  road,  the  lower  course 
should  be  increased  in  thickness  or  an  additional  course  of 
broken  stone  should  be  used.  This  extra  layer,  sometimes  called 
the  subbottom  course,  varies  from  3  to  18  inches  in  thickness 
and  is  composed  of  the  largest  sized  products  of  the  crusher  or 
large  field-stone,  broken  boulders,  or  ledge  stone.  Gravel,  slag, 
brickbats,  cinders,  or  clinker  are  often  substituted  for  the  broken 
stone  in  foundation  courses. 

Cement-Concrete  Foundations.  Concrete  foundations  should 
ordinarily  be  used  under  all  types  of  stone  block,  brick, 
sheet  asphalt,  and  bituminous  concrete  pavements.  The  thick- 
ness of  the  concrete  foundation  varies  from  4  to  8  inches, 
6  inches  usually  being  employed.  An  8-inch  foundation  is 


GRADING,  DRAINAGE,   AND  FOUNDATIONS  123 

necessary  only  when  the  subsoil  is  extremely  poor  or  the 
traffic  exceptionally  heavy.  Whenever  a  concrete  foundation  is 
constructed,  traffic  should  be  kept  from  it  for  seven  to  ten  days  in 
order  to  allow  it  to  set  up  thoroughly.  Concrete  is  manufac- 
tured by  three  methods:  mixing,  in  situ,  and  grouting. 

The  Cement-Concrete.  Briefly  stated,  concrete  is  a  mixture 
of  water,  hydraulic  cement,  sand  or  other  fine  material,  and 
broken  stone  or  gravel  or  similar  material.  The  best  and  strong- 
est concrete  will  result  when  the  sand  is  sufficient  in  quantity 
to  just  fill  the  voids  in  the  stone,  and  enough  cement  is  used  to 
fill  the  voids  in  the  sand  and  stone.  An  accurate  proportioning 
of  the  materials  can  be  made  only  by  carefully  determining  the 
voids  of  the  various  ingredients,  and  since  the  sand,  stone,  and 
gravel  are  quite  variable  in  this  respect,  frequent  determina- 
tions should  be  made.  It  is  customary  in  practice  to  adopt 
certain  definite  proportions  such  as  1:2  15,  i  13  :  6,  or  i  :  2^  :  7; 
the  first  figure  indicating  the  number  of  parts  of  cement;  the 
second  figure,  the  parts  of  sand  or  fine  aggregate;  and  the  third, 
the  parts  of  the  coarse  aggregate.  Two  kinds  of  cement  are 
used,  namely,  Portland  and  natural,  there  being  many  brands 
of  each.  A  natural  cement  does  not  produce  so  strong  a  con- 
crete and  it  obtains  its  initial  set  much  quicker  than  a  Portland 
cement.  On  this  account,  and  due  to  the  fact  that  the  two 
cements  are  nearly  equal  in  price,  Portland  cement  is  usually 
specified  to  be  used  in  all  classes  of  concrete  foundations. 

Mixing  Method.  The  cost  of  a  concrete  foundation  con- 
structed by  the  mixing  method  will  vary,  depending  upon  the 
richness  of  the  mix  used,  the  handling  of  the  different  materials 
preliminary  and  subsequent  to  the  mixing,  and  upon  the  method 
of  mixing. 

The  proportions  having  been  adopted,  the  various  ingredients 
are  measured  out  by  volume  and  mixed  together  with  water 
until  the  desired  consistency  is  obtained.  A  mixture  which  may 
be  easily  placed  with  good  results  will  be  obtained  if  enough 
water  is  used  so  that  the  resultant  concrete  is  somewhat  sloppy, 
but  not  so  much  so  that  any  of  the  water  will  run  away  from  it, 
or  so  much  as  will  cause  a  segregation  of  the  ingredients.  The 


124  ELEMENTS   OF  HIGHWAY  ENGINEERING 

concrete  thus  mixed  is  placed  upon  the  prepared  roadbed  to 
the  required  thickness.  The  concrete  is  then  tamped  and 
smoothed  with  the  backs  of  shovels  until  the  free  mortar  rises 
to  the  surface.  Since  in  the  majority  of  types  of  pavements  a 
layer  of  some  kind  of  material  is  interposed  between  the  sur- 
face of  the  foundation  and  the  wearing  course  material,  any 
very  slight  irregularities  in  the  surface  of  the  foundation  will 
not  cause  trouble.  When  a  smooth  surface  is  required  the  con- 
crete should  be  struck  with  a  template  that  will  give  the  desired 
shape.  Care  should  also  be  taken  in  conveying  the  concrete 
from  the  place  where  it  is  mixed  to  the  place  where  it  is  de- 
posited to  see  that  none  of  the  ingredients  are  segregated.  When 
the  foundation  is  completed  it  should  be  kept  moist  for  at  least 
two  or  three  days.  When  the  sun  is  extremely  hot,  it  may 
also  be  necessary  to  cover  the  concrete  during  this  period. 

Hand  Mixing.  One  method  of  hand  mixing  is  to  spread 
the  sand  for  a  batch  in  a  thin  layer  in  the  form  of  a  square  or  a 
rectangle  on  the  mixing  platform  of  boards  finished  with  a 
smooth  and  tight  surface.  The  required  amount  of  cement  is 
then  spread  out  on  the  sand  and  the  two  are  turned  with  shovels 
in  a  dry  state  until  thoroughly  mixed.  Water  is  then  added 
and  mixed  with  the  sand  and  cement,  thus  making  a  mortar. 
The  mortar  is  spread  out  in  a  thin  layer  in  a  manner  similar 
to  the  way  the  sand  was  first  spread.  The  required  amount  of 
coarse  aggregate,  which  has  been  previously  wet  down,  is  then 
brought  to  the  platform  and  spread  out  over  this  layer  of  mortar. 
The  mortar  and  the  coarse  aggregate  are  then  turned  until 
thoroughly  mixed. 

Machine  Mixing.  The  concrete  mixing  machine  employed 
in  paving  work  is  of  the  batch  or  the  continuous  mixer  type.  One 
of  the  main  objections  to  a  continuous  mixer  is  the  uncertainty 
of  securing  the  right  proportions  of  the  ingredients.  In  the 
continuous  machines  the  mixing  is  generally  accomplished  by 
means  of  paddles  fixed  to  a  revolving  shaft  which  mixes  the 
materials  together  as  they  fall  into  the  mixing  trough  and  at 
the  same  time  pushes  them  toward  the  discharge  end.  Water 
is  added  to  the  mass  when  it  reaches  the  mixing  trough.  In  the 


GRADING,   DRAINAGE,   AND   FOUNDATIONS 


125 


case  of  batch  mixers  each  batch  of  concrete  is  mixed  separately 
and  the  mechanism  does  not  have  to  be  depended  upon  for  the 
accurate  proportioning  of  the  mix.  There  are  several  types, 
similar  to  that  shown  in  Fig.  51,  which  are  portable  and  espe- 
cially designed  for  paving  work.  The  mixing  drums  of  batch 
mixers  vary  in  shape,  some  being  cylindrical,  others  cubical, 


FIG.  51.     Koehring  Cement-Concrete  Mixer. 

and  still  others  conical.  In  all  types  the  drum  revolves,  turning 
the  concrete  over  and  over.  Some  machines  are  equipped  with  a 
swinging  steel  boom  upon  which  a  bucket  travels.  With  this 
arrangement  the  concrete  may  be  distributed  within  the  area 
which  can  be  reached  by  the  boom. 

The  contract  price  of  a  i  :  3  :  6  concrete  foundation,  mixed 
and  placed,  varies  from  $5  to  $7  per  cubic  yard  or  from  about 
83  cents  to  $1.1 6  per  square  yard,  if  the  foundation  is  6  inches 
thick. 

In  Situ  Method.  A  second  method  of  construction,  known 
as  in  situ,  consists  of  spreading  and  rolling  a  layer  of  broken 
stone  of  the  required  thickness  in  a  manner  similar  to  the  con- 
struction of  the  bottom  course  of  an  ordinary  broken  stone  road. 
A  i  :  3  mixture  of  cement  and  sand  in  a  dry  state  is  spread 
over  the  surface  and  swept  into  the  voids.  The  surface  is  flushed 


126  ELEMENTS   OF   HIGHWAY   ENGINEERING 

with  water,  rolled,  and  more  dry  mortar  spread  during  flushing 
and  rolling  until  all  voids  are  filled. 

Grouting  Method.  In  a  third  method  a  layer  of  broken  stone, 
of  sufficient  depth  to  make  the  requisite  thickness  of  concrete, 
is  deposited  on  the  subgrade.  The  layer  is  thoroughly  rolled  and 
is  then  poured  with  a  grout  composed  of  one  part  cement  to  four 
parts  sand.  The  grouting  and  rolling  are  continued  until  the 
voids  in  the  stone  are  filled.  The  Hassam  Paving  Co.,  of  Worces- 
ter, Mass.,  use  special  grout-mixing  tanks  in  connection  with  this 
kind  of  work.  The  grout  flows  from  these  tanks  through  a  spout 
to  the  point  on  the  road  where  it  is  to  be  used. 

Foundations  Over  Marshes.  Sometimes  it  becomes  neces- 
sary to  carry  a  road  across  marsh  land  which  is  so  unstable  that 
a  crowbar  will  sink  into  it.  When  the  topography  of  the  land 
is  such  that  there  is  no  opportunity  for  subdrainage,  some  sup- 
port must  be  provided  for  the  embankment.  Usually  there  will 
be  more  or  less  settlement,  and  hence  no  improved  form  of 
surfacing  should  be  placed  on  the  fill  until  all  settlement  has 
ceased. 

Old  Pavements  as  Foundations.  In  New  York  City  and 
some  other  municipalities  old  stone  block  pavements  have  been 
used  as  foundations  for  sheet  asphalt  pavements.  In  some  cases, 
in  order  to  provide  room  for  the  asphalt  wearing  course,  the 
blocks  were  taken  up  and  relaid  on  their  sides.  It  is  contended 
that  a  large  percentage  of  the  repair  work  on  the  asphalt  pave- 
ments in  these  places  is  due  to  the  fact  that  there  is  more  or 
less  movement  of  the  blocks. 

Bituminous  Concrete  Foundations.  A  bituminous  concrete 
foundation  has  been  used  to. some  extent  as  a  substitute  for  a 
hydraulic  cement-concrete  foundation  for  sheet  asphalt  and  other 
bituminous  concrete  pavements.  Probably  the  first  construction 
of  this  kind  was  used  in  Washington,  D.  C.,  from  1872  to  1887, 
when  coal-tar  pavements  were  laid  quite  extensively  in  that 
city.  In  Omaha,  in  1891,  a  6-inch  bituminous  foundation  for 
an  asphalt  pavement  was  built  of  broken  stone  and  gravel  thor- 
oughly mixed  with  asphalt.  Foundations  of  a  similar  character 
are  sometimes  used  to-day.  They  are  not  as  strong,  however, 


GRADING,   DRAINAGE,   AND  FOUNDATIONS  127 

as  those  of  hydraulic  cement-concrete  and  have, the  further 
objection  that  the  wearing  course  cannot  usually  be  removed 
without  disturbing  the  foundation. 

Foundations  for  bridges  and  sidewalks  will  be  considered 
under  the  chapters  especially  devoted  to  these  subjects. 


CHAPTER  VI 
EARTH  AND  SAND-CLAY  ROADS 

OCCURRENCE.  Earth  roads  comprise  about  90  per  cent  of 
the  total  road  mileage  in  the  United  States,  or  approximately 
2,000,000  miles.  Although  many  of  the  States  are  spending 
large  sums  of  money  in  constructing  highways  with  a  broken 
stone  or  gravel  surface  or  with  some  type  of  pavement,  it  is 
obvious  that  the  improvement  of  the  total  mileage  in  this  manner 
is  a  stupendous  task  and  not  warranted  from  the  standpoint 
of  either  economy  or  efficiency.  The  construction  and  main- 
tenance of  earth  roads  is  therefore  of  great  importance,  par- 
ticularly in  those  sections  of  the  country  where  money  or  road- 
building  materials,  such  as  stone  and  gravel,  are  wanting.  In 
some  States  the  solution  of  the  good  roads  problem  is  based 
mainly  upon  the  successful  construction  and  maintenance  of 
earth  roads. 

The  labors  of  those  who  have  made  the  improvement  of 
earth  roads  a  serious  study  have  led  to  the  construction  of 
sand-clay  roads  in  certain  sections.  This  type  has  been  built 
with  varying  degrees  of  success  in  different  parts  of  the  country, 
the  total  mileage  in  the  United  States  being  about  25,000. 

SOILS 

The  formation  of  soils  and  their  classification  have  previously 
been  given  in  Chapter  V,  hence  in  this  chapter  only  their  rela- 
tion to  the  construction  and  maintenance  of  earth  roads  will 
be  considered.  The  soil  conditions  in  different  parts  of  the 
country  and  even  in  restricted  localities  are  so  variable  that 
what  may  be  an  advisable  method  of  construction  in  one  place 
will  not  serve  in  another.  Therefore  a  careful  examination  of 
the  soil  is  essential. 

128  • 


EARTH  AND   SAND-CLAY  ROADS  129 

SAND.  Sand  is  practically  the  only  soil  that  makes  a  better 
road  surface  in  a  wet  than  in  a  dry  condition.  This  fact  is  well 
illustrated  by  the  wet  sand  on  a  beach  between  low  and 
high  water  marks.  It  is  possible  to  draw  loads  over  this  sur- 
face without  difficulty.  A  sandy  road  when  dry,  however,  is 
as  objectionable  as  a  road  of  clayey  soil  when  wet. 

CLAY.  Clays  are  of  two  kinds,  ball  clay  and  slaking  clay. 
The  ball  clay  is  extremely  plastic  and,  as  its  name  implies, 
tends  to  ball  or  lump  up.  It  will  keep  its  shape  even  if  im- 
mersed in  water  for  some  time.  A  slaking  clay,  on  the  other 
hand,  does  not  have  this  same  power  of  plasticity  and  is  more 
crumbly  in  its  nature,  and  more  readily  miscible  with  water. 
It  is  apparent  that  the  slaking  clays  do  not  possess  the  binding 
power  of  the  ball  clays.  A  soil  which  is  largely  composed  of 
clay  acts  just  the  opposite  from  sand  under  the  same  climatic 
conditions.  In  dry  weather  the  surface  becomes  hard  and  if 
kept  in  proper  shape  makes  a  good  surface.  In  continued  wet 
weather,  however,  the  water  soaks  into  the  clay  and  softens  it, 
with  the  result  that  the  surface  no  longer  can  support  the  traffic. 

SAND-CLAY.  An  earth  road  in  which  the  surface  is  com- 
posed of  a  soil  that  is  a  mixture  of  sand  and  clay  will  be  much 
more  satisfactory,  under  most  conditions,  than  one  composed 
of  either  of  these  soils  alone.  There  are  many  places  through- 
out the  country  where  a  top  soil  is  found  which  is  a  mixture 
of  these  two  materials  and  which  serves  to  make  an  excellent 
road.  Suitable  top  soils  of  this  character  should  be  composed 
of  a  mixture  of  clay  and  sand  or  gravel  which  shall  not  contain 
stones  over  2^  inches  in  diameter  or  an  excess  of  fine  sand. 
The  material  passing  a  one-hundred  mesh  sieve  should  be  plastic 
when  mixed  with  a  small  amount  of  water. 

CONSTRUCTION 

The  construction  of  earth  and  sand-clay  roads  consists  of 
providing  proper  drainage  through  the  medium  of  culverts  and 
drains  and  the  formation  of  the  wearing  course. 

DRAINAGE.    One  of  the  principal  faults  with  a  large  majority 


130  ELEMENTS   OF  HIGHWAY  ENGINEERING 

of  the  earth  roads  in  this  country  is  that  they  are  not  properly 
drained.  The  want  of  proper  drainage  allows  the  surface  to 
become  soft  after  rains  and  at  times  when  the  frost  is  coming 
out  of  the  ground,  with  the  result  that  the  traffic  soon  cuts 
through  and  in  some  cases  the  roads  become  practically  im- 
passable. If  subdrains  are  employed  in  an  intelligent  manner, 
if  the  surface  is  kept  shaped  up  so  as  to  throw  the  water  to 
the  side  ditches,  and  if  the  culverts  and  ditches  are  properly 
constructed  and  maintained,  there  is  no  difficulty  in  making  an 
earth  road  readily  passable  at  all  times  of  year  to  the  traffic 
for  which  it  is  suitable. 

General  methods  of  constructing  subdrains  have  been  de- 
scribed in  Chapter  V. 

The  surface  drainage  is  accomplished  by  means  of  the  longi- 
tudinal grade,  the  crown  of  the  road,  and  the  side  ditches. 
If  practicable  the  longitudinal  grade  should  not  be  over  4  per- 
cent and  under  no  conditions  over  6  percent.  The  surfaces  of 
earth  roads  having  grades  over  4  percent  are  expensive  to  main- 
tain after  heavy  rains  on  account  of  the  consequent  erosion  of 
the  surface  by  rapidly  flowing  water.  Figs.  52  and  53  show 
typical  cross-sections  of  earth  roads.  The  cross-section  should 
be  of  such  form  as  will  render  practicable  the  economic  use  of 
the  standard  types  of  grading  machines  described  in  Chapter  V. 
The  sections  should  be  varied  with  the  grade  as  indicated  by 
the  illustrations  of  cross-section.  The  design  shown  in  Fig.  54 
is  based  upon  the  conclusion  that  erosion  of  earth  ditches  will 
usually  occur  on  grades  of  over  4  percent.  Since  the  surface 
of  an  earth  or  sand-clay  road  is  not  as  impervious  as  those 
constructed  with  a  material  such  as  stone  or  gravel,  it  is  gener- 
ally given  more  crown.  An  average  crown  of  about  one  inch  to 
the  foot  is  common,  the  surface  being  shaped  to  follow  a  circular 
or  other  curve  or  else  formed  by  two  or  more  intersecting  planes. 
In  no  case  should  the  ditches  be  less  than  6  feet  in  width,  as 
narrow  ditches  soon  become  clogged  and  unable  to  readily 
carry  off  the  surface  water,  with  the  result  that  the  water  seeps 
into  the  roadway.  The  depth  of  the  ditch  should  be  at  least 
2  feet  6  inches  below  the  center  of  the  surface  of  the*  roadway 


EARTH  AND    SAND-CLAY   ROADS 


131 


Longitudinal 
Tile  Drain 


Courtesy  of  the  Engineering  News. 

.FiG.  52.     Iowa  State  Highway  Commission  Cross- Section  for  Earth  Roads 
Having  Grades  of  2  Percent  or  Less. 


Courtesy  of  the  Engineering  News. 

FIG.  53.     Iowa  State  Highway  Commission  Cross-Section  for  Earth  Roads 
Having  Grades  Over  2  Percent  but  Less  Than  4  Percent. 


Courtesy  of  the  Engineering  News. 

FIG.  54.     Iowa  State  Highway  Commission  Cross-Section  for  Earth  Roads 
Having  Grades  of  4  Percent  or  More. 


132  ELEMENTS   OF   HIGHWAY   ENGINEERING 

in  order  to  provide  ample  waterway.  Offtake  ditches  or  other 
outlets  for  the  water  flowing  in  the  longitudinal  ditches  should 
be  provided,  as  otherwise  the  volume  of  water  will  exceed  the 
capacity  of  the  ditches. 

WEARING  COURSE  OF  EARTH  ROADS.  The  method  of  con- 
structing the  wearing  course  of  earth  roads  varies  with  the 
machines  available.  The  fundamentals  of  construction  with 
adequate  plant  equipment  are  well  illustrated  by  the  practice 
of  the  Iowa  State  Highway  Commission  as  described  by  Prof. 
T.  R.  Agg.* 

"There  are  the  three  following  classes  of  roads  encountered 
in  the  various  counties  in  Iowa  where  the  elevating  grader  has 
proven  satisfactory: 

"(i)  Roads  practically  level  where  the  new  grade  line  is 
parallel  to  the  profile  on  the  old  road,  there  being  only  a  few 
knolls  to  be  removed. 

"(2)  Roads  on  which  there  are  a  succession  of  knolls  and 
consequently  a  succession  of  cuts  and  fills  most  of  which  do 
not  exceed  about  two  feet  in  depth. 

"(3)  Roads  where  extensive  grade-reduction  work  must  be 
done. 

"The  outfit  necessary  for  roads  of  Class  i  consists  ot  the 
elevating  grader  drawn  by  6  or  8  teams  or  by  a  tractor,  a  blade 
grader,  a  few  slips  or  wheelers,  a  heavy  disk  harrow,  a  heavy 
straight-tooth  harrow,  and  a  split-log  or  plank  drag.  If  a  roller 
is  also  available  a  better  road  can  be  constructed  than  is  possible 
without  it.  For  roads  of  Classes  2  and  3,  a  number  of  dump- 
wagons  are  also  necessary. 

"In  starting  the  construction  the  first  cut  is  taKen  at  tne 
shoulder  line,  and  the  material  thus  removed  is  deposited  near 
the  shoulder  line  of  the  opposite  side  of  the  road,  but,  of  course, 
in  the  roadway. 

"Stakes  are  set  for  the  first  cut  so  that  the  driver  can  follow 
them  conveniently.  If  the  outfit  is  horse-drawn,  the  stakes  are 
set  so  that  the  tongue  of  the  elevating  grader  will  follow  them. 

*From  Engineering  News,  April  16,  1914. 


EARTH  AND   SAND-CLAY   ROADS  133 

If  the  grader  is  drawn  by  a  tractor,  they  are  set.  so  that  the 
front  wheel  on  the  steering  side  will  follow  them.  The  exact 
distance  of  these  stakes  from  the  line  of  the  cut  will  vary  some- 
what with  the  type  of  elevating  grader  used,  and  must  be 
determined  before  the  stakes  are  set. 

"The  first  cut  is  a  light  one  and  usually  one  horse  of  the  lead 
team  follows  this  first  furrow  and  thereby  guides  the  grader 
in  making  the  succeeding  cut.  If  the  grader  is  drawn  by  a 
tractor,  a  side  hitch  is  used  so  that  the  tractor  travels  on  the 
'land'  side,  and  a  plumb  bob  is  hung  from  the  tractor  in  such 
a  position  that  it  will  follow  the  furrow  and  thus  serve  to  assist 
the  driver  in  steering. 

"On  roads  of  Class  i,  the  successive  rounds  of  the  elevating 
grader  are  made  without  reference  to  the  slight  knolls  that 
occur;  and  the  material  deposited  on  the  roadway  on  top  of 
the  knolls  is  hauled  away  by  slips  or  wheelers,  while  the  elevat- 
ing grader  is  cpmpleting  its  round.  A  suitable  adjustment  of 
the  working  forces  can  be  made  so  that  the  slips  or  wheelers 
can  be  kept  up  with  the  grader. 

"On  roads  of  Class  2,  teams  with  dump-wagons  follow  the 
elevating  grader,  loading  where  cuts  are  to  be  made  and  dump- 
ing the  materials  in  the  fills,  the  elevating  grader  continuing 
its  rounds  and  depositing  directly  on  the  road  in  the  low  places. 
Here  again  a  suitable  adjustment  of  working  forces  must  be 
made  so  that  the  elevating  grader  will  not  have  to  wait  for  the 
wagons.  It  is  more  economical,  however,  to  construct  a  mile 
or  more  of  road  at  a  time  than  it  is  to  turn  the  elevating  grader 
constantly,  as  would  be  necessary  if  each  cut  were  completed 
by  itself. 

"On  roads  of  Class  3,  the  elevating  grader  is  simply  used  as 
a  loader  for  the  wagons,  and  each  cut  is  completed  by  itself. 
The  economy  of  the  grader  in  this  case  depends  upon  the  steep- 
ness of  the  grade  and  the  room  for  maneuvering. 

"As  the  elevating  grader  makes  successive  rounds  it  gets 
farther  away  from  the  center  of  the  road  and,  consequently, 
when  it  is  at  the  deepest  part  of  the  ditch  where  the  heaviest 
cutting  is  being  done  the  earth  is  deposited  in  the  middle  of 


134  ELEMENTS   OF  HIGHWAY   ENGINEERING 

the  road,  where  the  greatest  filling  is  necessary  to  give  the  crown. 

"The  material  deposited  on  the  roadway  will  consist  of  many 
large  lumps  as  well  as  of  sods  and  fine  material.  To  work  this 
material  down  to  a  surface  that  can  be  travelled,  the  clods  and 
sods  must  be  broken  up  with  a  disk  harrow  until  small  enough 
to  form  a  satisfactory  surface.  Often  the  sods  and  weeds  are 
collected  by  harrowing  with  a  stiff-tooth  harrow  and  thrown 
out  with  pitchforks. 

"To  bring  the  surface  to  its  final  shape  a  few  rounds  must 
be  made  with  a  blade  grader.  Then,  after  the  first  rain,  the 
surface  is  smoothed  with  a  road  drag  and,  when  partially  dry, 
rolled.  Constant  dragging  is  necessary  during  the  first  year  to 
keep  the  road  in  shape  while  it  is  becoming  compacted  by 
traffic. 

"The  cost  of  constructing  earth  roads  by  this  method  varies 
from  about  $100  per  mile  for  Class  i  roads,  to  $250  per  mile 
for  Class  2;  while  the  cost  of  Class  3  is  an  exceedingly  variable 
quantity,  as  is  apparent  from  the  nature  of  the  work.  As  an 
average  of  the  work  done  by  some  of  the  well  organized  counties, 
$150  per  mile  may  be  taken." 

WEARING  COURSE  OF  SAND-CLAY  ROADS.  Top-Soil  Roads. 
Many  miles  of  roads  in  the  South  have  been  surfaced 
with  from  6  to  14  inches  of  top  soil,  consisting  of  a  mix- 
ture of  sand  and  clay  taken  from  the  adjacent  fields. 
*  "The  subgrade  of  the  roadway  is  brought  to  a  level  or  slightly 
convex  cross-section.  The  sand-clay  is  then  placed  in  a  con- 
tinuous layer,  from  10  to  12  inches  thick,  the  material  being 
spread  as  fast  as  delivered  and  not  dumped  in  piles  here  and 
there.  This  layer  is  spread  for  a  width  of  20  feet  for  a  nominal 
30-foot  roadway.  After  a  sufficient  quantity  has  been  placed 
in  this  manner,  an  ordinary  road  machine  is  drawn  along  the 
ditch  line,  cutting  about  four  inches  deep  at  the  outside,  and 
the  blade  is  set  so  as  to  cast  the  material  from  the  ditch  against 
the  edge  of  the  sand-clay  layer.  In  this  way  a  shoulder  is 
built  up  against  the  sand-clay  to  hold  it  in  place.  This  also 
shapes  the  ditch.  After  both  sides  have  been  thus  shaped,  the 

*By  John  C.  Koch,  1914  Proceedings,  Am.  Soc.  C.  E.,  page  295. 


EARTH  AND    SAND-CLAY   ROADS  135 

road  machine,  in  successive  passages,  rounds  up  the  cross-section 
of  the  sand-clay  so  as  to  give  proper  crown  to  the  roadway  and  a 
smooth  line  from  the  crown  to  the  ditches.  As  soon  as  the 
road  is  shaped,  traffic  and  the  construction  teams  begin  to 
compact  it,  and  it  rapidly  becomes  consolidated  without  the 
use  of  a  road  roller.  As  the  consolidation  progresses,  ruts  are 
formed,  and  they  should  be  rilled  and  a  proper  cross-section 
maintained  by  the  occasional  use  of  the  road  machine  for  a 
period  of  about  two  months.  Unless  this  is  done,  the  road 
surface  will  become  rutted  and  rough,  and  eventually  /com- 
pacted with  a  concave  crown  which  will  prevent  proper  drain- 
age. After  the  material  has  been  consolidated  into  a  hard  mass, 
the  difficulty  of  securing  a  good  cross-section  is  largely  increased. 

"The  cross-section  which  seems  to  have  given  the  most  gen- 
erally satisfactory  results  is  a  parabolic  form  with  a  crown  of 
%  inch  per  foot,  that  is,  for  a  roadway  surfaced  for  a  width 
of  20  feet,  the  crown  would  be  5  inches,  and  the  height  of  the 
center  of  the  road  above  the  ditch  (for  a  road  having  a  width 
of  30  feet  between  ditches)  would  be  7^  inches.  With  steeper 
crowns  than  this  it  has  been  found  that  the  surface  cuts  into 
a  series  of  parallel  ridges  running  from  the  wheel  tracks  to  the 
ditches  and  making  it  very  disagreeable  for  travel.  If  less 
crown  is  given,  the  provision  for  wear  is  too  small,  and  the 
drainage  may  not  prove  satisfactory  after  a  comparatively 
short  time. 

"There  are  many  miles  of  sand-clay  roads  in  Georgia  which 
have  cost  less  than  $500  per  mile  for  the  surfacing  in  place. 
They  carry  heavy  country  traffic,  and  the  repairs,  during  a 
period  of  5  years,  have  not  averaged  $5  per  mile  per  year." 

Roads  with  Sandy  Subsoil.  If  a  sand-clay  road  is  to  be 
constructed  of  a  sandy  subsoil,  the  roadbed  is  shaped  up  to 
the  desired  crown.  The  clay  is  brought  onto  the  road  and 
spread  in  a  layer  of  6  to  10  inches  at  the  center,  tapering  off 
to  a  thin  layer  at  the  sides.  If  the  construction  is  begun  at 
the  end  of  the  road  near  the  source  of  supply  of  the  clay,  the 
road  will  be  somewhat  compacted  during  construction  by  the 
teams  on  the  work.  It  is  necessary  that  the  clay  be  thoroughly 


136  ELEMENTS   OF  HIGHWAY  ENGINEERING 

mixed  with  the  sand  and  that  all  lumps  should  be  broken  up. 
Dry  mixing  or  covering  the  clay  layer  with  sand  and  leaving  it 
for  traffic  to  mix  and  compact  will  not  secure  as  quick  and  as 
good  results  as  can  be  obtained  by  plowing,  harrowing,  and 
rolling.  The  clay  should  be  puddled  to  secure  a  thorough  mix 
with  the  sand  and  hence  water  is  essential  to  obtain  the  best 
construction.  If  no  water  is  at  hand,  the  mixing  should  be 
completed  soon  after  or  during  rainy  weather. 

Roads  with  Clayey  Subsoil.  If  a  sand-clay  road  is  to  be 
constructed  of  a  clayey  subsoil,  the  roadbed  is  shaped  up  and 
drained  as  in  the  previous  case.  The  surface  is  then  plowed 
and  pulverized  as  much  as  possible  to  a  depth  of  4  inches.  This 
surface  is  covered  with  a  layer  of  sand  6  to  8  inches  thick.  In 
this  case  the  mixing  of  the  clay  and  the  sand  should  be  carried 
out  while  the  materials  are  in  a  dry  state.  After  this  prelimi- 
nary mixing  has  been  accomplished,  the  further  mixing  is  carried 
on  when  the  road  is  wet.  The  road  is  finally  shaped  up  and 
compacted.  It  must  not  be  expected  that  as  soon  as  a  sand-clay 
road  is  completed  it  will  give  a  perfect  surface.  It  is  only  by 
carefully  watching  the  road  and  adding  sand  or  clay  as  required 
that  a  satisfactory  surface  will  finally  be  obtained. 

BURNT  CLAY  ROADS.  In  order  to  improve  the  roads  in 
some  parts  of  the  Southern  States  where  there  is  no  sand,  ex- 
perimental sections  have  been  constructed  by  burning  the  very 
plastic  clay  of  which  the  roads  are  composed.  The  material 
is  plowed  up  and  is  piled  over  a  low  crib  work  of  firewood. 
Alternate  layers  of  wood  and  earth  are  built  up  until  a  height 
of  about  3  feet  is  obtained.  The  length  fired  at  any  one 
time  depends  upon  the  number  of  men  available.  When  the 
wood  burns  out  the  hardened  clay  is  shaped  up  and  compacted. 

STRAW  ROADS.  In  the  State  of  Washington  clay  roads 
have  been  improved  by  shaping  and  harrowing  the  road  to  a 
smooth  surface  and  then  applying  a  layer  of  wet  wheat  straw 
about  6  inches  thick.  The  straw  is  cut  and  mixed  with  the 
earth  by  means  of  a  disk  harrow.  The  roadway  is  compacted 
with  a  steam  roller.  It  has  been  found  necessary  to  treat  the 
roads  in  this  manner  about  twice  each  year. 


EARTH  AND  SAND-CLAY  ROADS 


137 


PETROLITHIC  ROADS.  This  type  of  road  is  formed  by  mixing 
the  soil  in  situ  with  a  bituminous  material.  The  earth  is  plowed 
up  to  a  depth  of  at  least  6  inches  and  is  thoroughly  pulverized, 
cultivated,  and  sprinkled  with  water.  Asphaltic  oil  is  applied 
in  one  to  two  coats  in  the  amount  of  one  gallon  per  square  yard. 
The  surface  is  recrowned  with  a  road  grader  and  tamped  with 
a  sheep's  foot  roller-tamper. 

In  many  cases  a  layer  of  broken  stone  or  screened  gravel 
is  spread  over  the  roadway  and  treated  with  about  %  gallon 


FlG.  55.     An  Earth  Road  Under  Poor  Maintenance. 

of  asphaltic  oil.  The  surface  is  then  thoroughly  harrowed  and 
rolled.  Another  treatment  of  oil  is  applied  at  the  rate  of  y± 
gallon  per  square  yard  and  a  ^-inch  layer  of  stone  screenings 
or  pea  gravel  is  then  spread  over  the  surface  and  rolled  with  a 
smooth-faced  roller. 

MAINTENANCE 

The  principal  work  in  maintaining  an  earth  road  is  to  keep 
the  surface  smooth  and  well  crowned  so  as  to  shed  water  as 
rapidly  as  possible.  If  any  depression  forms  in  the  surface, 
water  settles  in  it  and  softens  the  road,  with  the  result  that  a 


138 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


very  small  depression  will  work  into  a  large  and  dangerous 
hole  if  not  taken  care  of  at  once.  In  repairing  holes  in  an 
earth  road,  they  should  be  filled  with  the  same  kind  of  material 
that  is  used  in  the  surface,  since  if  a  harder  material  than  the 
surrounding  earth  is  used,  the  surface  will  tend  to  wear  un- 


FIG.  56.     An  Earth  Road  Under  Good  Maintenance. 

evenly  at  this  point,  due  to  the  harder  material  offering  more 
resistance  to  traffic.  An  earth  road  should  have  plenty  of  sun- 
light and  air,  and  hence  the  undergrowth  at  the  sides  should  be 
kept  cut.  Ditches  and  culverts  should  always  be  kept  clean 
to  give  an  easy  outlet  to  the  water. 

DRAGS  vs.  SCRAPERS.  A  large  part  of  the  maintenance 
work,  which  consists  in  keeping  the  road  in  shape,  can  be  done 
either  by  road  scrapers  and  graders  or  by  road  drags.  Different 
types  of  these  machines  have  been  described  in  Chapter  V. 
The  road  drag  has  been  the  salvation  of  the  earth  road.  An 
earth  road  needs  frequent  care,  and  since  drags  can  be  obtained 
at  an  extremely  low  cost,  it  is  possible  for  each  resident  along 
the  road  to  own  one.  By  having  one  drag  to  every  2  to  4  miles 
of  road  or  less,  and  encouraging  the  people  to  use  them  fre- 
quently, the  surface  can  be  kept  in  a  good  condition  all  the 


EARTH  AND    SAND-CLAY   ROADS  139 

time.  One  man  with  team  and  drag  can  keep  20  miles  in  good 
condition.  Where  road  scrapers  are  employed,  their  number 
is  generally  limited  so  that  it  is  only  possible  to  use  them  peri- 
odically a  few  times  each  year  on  the  roads  in  a  community. 
Frequently  the  surface  may  have  become  so  badly  worn  that 
considerable  work  is  necessary  to  get  the  road  in  good  shape 
again.  If  enough  scrapers  were  available  so  that  repairs  could 
be  made  at  opportune  times  from  the  standpoint  of  the  good 
of  the  road,  the  results  obtained  would  probably  be  fully  as 
good  as  those  obtained  by  using  road  drags,  but  the  cost  of 
maintenance  would  be  increased. 

ROAD  DRAG  LAW.  The  General  Assembly  of  the  State  of 
Illinois,  in  1908,  passed  a  Road  Drag  Law  authorizing  the  road 
commissioners  in  any  township  to  have  earth  roads  dragged  at 
all  seasons  of  the  year  whenever  it  was  deemed  to  be  beneficial, 
and  to  contract  with  the  adjoining  land  owners  for  this  work 
at  a  rate  of  from  75  cents  to  $i  per  mile,  not  less  than  20  feet 
wide,  for  each  time  the  road  was  dragged,  the  higher  price  to 
be  paid  for  work  done  during  the  months  of  December,  January, 
February,  or  March.  The  law  also  provides  it  to  be  unlawful 
to  place  loose  earth,  weeds,  sods,  or  other  vegetable  matter  on 
a  road  which  has  been  dragged  without  the  authority  of  the 
road  officials;  to  place  any  material  which  will  prevent  the 
free  flow  of  water;  for  any  traffic  to  pass  over  a  surface  just 
dragged  until  same  shall  have  partially  dried  out  or  have  frozen, 
except  in  those  instances  where  the  road  is  not  sufficiently  wide 
to  provide  a  safe  by-pass  or  on  roads  wide  enough  so  that  the 
wheels  will  not  make  a  rut  nearer  than  9  feet  to  the  center  of 
the  dragged  portion. 

In  order  that  all  commissioners  should  follow  the  same  prac- 
tice, the  following  instructions  were  published: 

"Roads  properly  dragged  will  dry  out  weeks  earlier  in  the 
spring  than  a  road  not  so  maintained,  and  when  dried  out  will 
be  smooth  and  in  excellent  condition.  Moreover,  they  will  not 
rut  up  so  readily  during  the  winter.  The  ordinary  country 
road  can  be  well  maintained  if  dragged  at  the  proper  time 
on  an  average  of  twice  a  month.  The  dragging  will  have 


140  ELEMENTS   OF  HIGHWAY  ENGINEERING 

to     be    more   frequent   during    winter    and    spring    than    in 
summer. 

"Unless  the  road  is  in  the  right  condition,  the  work  of  drag- 
ging will  be  wasted.  One  thing  to  be  insisted  upon  is  that  the 
work  be  done  at  the  right  moment.  The  right  time  is  when 
the  road  is  wet.  The  muddier  it  is  the  better  the  results.  On 
a  road  that  is  in  extremely  bad  condition  where  the  mud  is 
very  deep,  it  is  probable  that  the  lap-plank  drag  can  be  worked 
to  better  advantage.  In  the  summer  time  and  in  the  early  fall, 
dragging  should  be  done  while  it  is  actually  raining,  for  unless 
the  rain  is  exceptionally  heavy  and  long  continued,  the  water 
will  penetrate  the  dry  roadbed  so  fast  that  the  surface  will  be 
comparatively  dry  when  the  drag  is  used  after  the  rain  has 
stopped,  with  the  result  that  the  road  surface  will  work  up  in 
crumbs.  When  this  happens  it  is  a  sign  the  road  is  too  dry. 
The  nearer  it  is  possible  to  spread  the  mud  over  the  road  as  a 
mortar,  much  in  the  same  way  a  mason  works  mortar  with  a 
trowel,  the  greater  the  improvement  produced.  Under  no  con- 
ditions should  a  road  be  dragged  when  it  is  dry.  This  merely 
crumbles  up  the  surface  and  makes  a  layer  of  the  loose  ma- 
terial which  quickly  becomes  dust  and,  when  wet,  is  turned  into 
mud  and  holds  the  water  on  the  surface  of  the  road.  Drag 
when  the  road  is  good  and  muddy.  Don't  drag  when  it  is  dry. 
Drag  whenever  possible  at  all  seasons  of  the  year.  If  a  road 
is  dragged  immediately  before  cold  weather,  it  will  freeze  in  a 
smooth  condition." 


CHAPTER  VII 
GRAVEL  ROADS 

DEVELOPMENT.  Highways  constructed  with  a  wearing 
course  of  gravel  have  proved  suitable  for  light  traffic.  In  some 
instances  where  the  traffic  consists  of  light  horse-drawn  vehicles 
and  touring  cars,  such  as  is  typical  of  the  traffic  on  park  boule- 
vards, the  gravel  road  has  proved  to  be  superior  to  the  broken 
stone  road  as  it  has  been  less  affected  by  motor-car  traffic  and 
is  more  easily  repaired. 

Gravel  roads  are  found  in  every  State  of  the  Union.  Through- 
out the  United  States  there  have  been  at  least  110,000  miles 
of  highways  improved  with  roadways  of  gravel.  As  there  are 
many  sections  where  rock  does  not  exist  from  which  to  manu- 
facture broken  stone,  the  development  of  gravel  roads  in  such 
localities  has  been  rapid.  In  some  parts  of  New  England  natural 
gravel  roads  exist,  generally  found  on  gravel  ridges. 

THE  GRAVEL 

DEFINITIONS.  Throughout  this  book  the  terms  gravel,  bank 
gravel,  sand,  and  clay  will  be  used  to  designate  the  materials 
described  in  the  following  definitions. 

Gravel.*  Small  stones  or  pebbles  which  will  not  pass  a 
lo-mesh  sieve. 

Rank  Gravel.*  Gravel  found  in  natural  deposits,  usually 
more  or  less  intermixed  with  sand,  clay,  etc.;  gravelly  clay, 
gravelly  sand,  clayey  gravel,  and  sandy  gravel  indicate  the 
varying  proportions  of  the  admixture  of  the  finer  materials. 

Sand.*f  Finely  divided  rock  detritus,  the  particles  of  which 
will  pass  a  lo-mesh  and  be  retained  on  a  2oo-mesh  sieve. 

Clay.*f  Finely  divided  earth,  generally  silicious  and  alumi- 
nous, which  will  pass  a  2oo-mesh  sieve. 

FORMATION  AND   OCCURRENCE.     Gravel  is  generally  found 

*  Proposed  in  1915  by  Committee  D-4,  American  Society  for  Testing 
Materials. 

fDec.,  1914  Proceedings,  Am.  Soc.  C.  E.,  pages  3013  to  3017. 

141 


142  ELEMENTS   OF   HIGHWAY  ENGINEERING 

mixed  with  sands  and  clays  in  varying  proportions.  Most  of  the 
gravel  in  the  northern  part  of  the  United  States  is  glacial  deposit. 
The  district  at  one  time  covered  by  the  glacier  included  all 
of  New  England  and  Canada  and  that  part  of  the  United  States 
north  of  a  line  running  from  a  point  just  south  of  New  York 
City  to  the  southwest  corner  of  New  York  State,  then  closely 
following  the  Ohio  River  to  the  Missouri  River  and  west- 
ward to  the  Pacific  coast.  This  immense  ice  sheet  in  its 
forward  movement  sheared  off  the  rocks  and  carried  them  along 
in  its  path.  With  the  melting  and  consequent  receding  of  the 
glacier,  the  materials  picked  up  in  its  path  were  deposited  and 
sometimes  further  distributed  by  the  water  from  the  melting 
ice.  On  account  of  the  large  variety  of  rocks  passed  over  by 
the  glacier  and  the  intermingling  and  mixing  of  the  worn  and 
abraded  pieces  by  the  water,  gravels  usually  vary  widely  in 
quality  and  composition.  The  glacial  rivers  aided  further  to 
break  up  and  distribute  the  debris  picked  up  by  the  glacier. 
The  larger  stones  are  generally  quite  hard,  since  the  softer 
stones  have  been  entirely  broken  up  by  the  abrasive  action. 
Such  hard  rocks  as  flint,  chert,  quartzite,  felsite,  granite, 
sandstone,  and  volcanic  rocks  occur  to  a  large  extent  in  gravels. 
Throughout  New  England,  the  Adirondack  district,  and  the 
Appalachian  belt  south  to  the  limit  of  the  ice  sheet  in  that 
direction,  a  "blue  gravel"  abounds,  so-called  because  it  is  made 
up  largely  of  trap  rock  which  was  crushed  by  the  glacier  and 
left  near  the  point  where  it  originally  existed,  and  hence  has 
not  been  much  affected  by  the  action  of  water.  Gravel  in 
which  the  stones  are  largely  composed  of  quartz  is  also  ex- 
tremely common,  both  in  New  England  and  some  of  the 
middle  western  States. 

REQUISITES  OF  GRAVEL.  A  gravel  to  make  a  good  road- 
building  material  should  be  composed  of  stones,  which  are  hard 
and  tough  and  hence  will  not  readily  disintegrate  under  traffic; 
that  vary  from  a  large  to  a  small  size,  the  proportions  of  the 
different  sizes  being  such  that  the  voids  will  be  a  minimum; 
and  that  contain  enough  binding  material  to  cement  the  whole 
mass  together. 


GRAVED  ROADS  143 

Gravel  composed  of  sharp,  angular  stones,  with  slight- 
ly roughened  surfaces,  has  given  particularly  satisfactory 
results. 

The  Binder.  Clay,  iron  oxide,  lime,  loam,  and  finely  di- 
vided silica  constitute  the  cementing  mediums  found  in  gravels. 
Frequently  a  mistake  is  made  in  selecting  a  gravel  that  will 
pack  quickly.  An  excess  of  20  percent  of  clay  in  the  mass  will 
produce  mud  during  a  continued  wet  spell.  Usually  16  per- 
cent of  clay  is  sufficient  to  bind  a  well  graded  gravel.  To  re- 
move an  excess  of  clay,  the  gravel  must  be  screened  and  some- 
times washed.  Iron  oxide  has  been  mentioned  as  one  of  the 
cementing  materials  found  in  some  gravels,  occurring  as  a  slight 
coating  on  the  pebbles.  Gravels  of  this  nature  make  an  ex- 
cellent road  material  and  sometimes  compact  much  more  firmly 
in  the  road  under  traffic  than  in  the  original  bed.  The  gravels 
from  Paducah,  Kentucky,  and  from  Shark  River  deposits  in 
New  Jersey  are  examples  of  this  type.  Similar  deposits,  in 
which  there  is  little  or  no  clay  present,  are  found  where  the 
cementing  material  is  a  lime  or  a  combination  of  lime  and  iron 
ore.  In  some  cases  small  pebbles,  which  will  crush  up  during 
the  construction  of  the  road  or  under  the  action  of  traffic, 
will  furnish  a  binder  that  firmly  cements  the  larger  stones 
together.  Loam  and  finely  divided  silica  also  compose  the  bind- 
ing material  in  some  deposits. 

As  a  general  rule  a  bank  gravel  is  better  than  a  stream  gravel 
because  its  particles  are  not  generally  so  smooth  and  because  it 
contains  more  fine  material  which  will  act  as  a  binder.  River 
gravel  contains  more  silica  than  a  bank  gravel  of  the  same 
locality,  since  the  clay  has  probably  been  washed  out.  A  gravel 
which  contains  too  much  fine  material  may  be  improved  by 
screening,  while  one  which  is  lacking  in  binding  material  can 
be  improved  by  adding  some  cementing  material  such  as  clay, 
shale,  marl,  loam,  or  stone  screenings.  An  indication  of  the 
binding  qualities  of  a  gravel  may  be  obtained  by  noticing  the 
gravel  in  the  bank.  Usually,  if  the  bank  faces  are  vertical, 
and  a  pick  is  required  to  dislodge  the  gravel,  and  large  chunks 
may  be  broken  out  in  which  the  smaller  pebbles  are  firmly 


144 


ELEMENTS   OF   HIGHWAY  ENGINEERING 


cemented  together,  the  gravel  will  make  a  satisfactory  road 
material. 

Testing  Gravel.  Unless  service  tests  have  proved  that  a 
gravel  from  a  particular  location  is  a  satisfactory  material,  the 
gravel  should  be  tested  before  being  used. 

Sampling.  Samples  of  gravel  should  be  taken  with  the  sand 
or  clay  just  as  it  occurs  in  the  stream  or  gravel  bank. 

Mechanical  Analysis.  The  proportions  of  the  various  sizes 
contained  in  any  one  sample  can  be  ascertained  by  screening 
the  sample  through  screens  and  sieves  of  different  sizes,  the 
proportions  retained  on  or  passing  any  screen  or  sieve  being 
determined  by  weight.  (See  Appendix  III.) 

The  screens  used  in  making  mechanical  analyses  of  gravel 
or  stone  are  usually  made  with  round  holes  having  diameters 
varying  from  3^  inches  to  ^4  of  an  inch  in  size.  The  sieves 
used  in  making  mechanical  analyses  of  sand  and  other  fine 
materials  are  made  of  wire  with  square  holes.  The  sizes  vary 
from  one  having  10  openings  to  the  linear  inch  down  to  one 
having  200  openings.  The  screens  with  square  holes  are 
designated  as  zo-mesh,  4O-mesh,  2oo-mesh,  etc.,  depending 
upon  the  number  of  openings  per  linear  inch.  The  stand- 
ard sizes  of  mesh  screens  for  testing  sand  adopted  by  the 
American  Society  for  Testing  Materials  are  given  in  the 
following  table: 


DIAMETER 

OF  WIRE 

MESHES  PER  LINEAR  INCH    (  —  2.54  CM.) 

Inch 

Mm. 

2OO     .           .  .                   

O.O0235 

o  .  05969 

100  

O.O04S 

o.  1143 

80  

O.OO575 

o.  1460 

so.  . 

O.OOQ 

0.22865 

40.  . 

O.OIO25 

0.26035 

T.Q 

O  OI^7S 

0.34925 

2O 

o  0165 

0.4191 

10                                

O.O27 

O.69S8 

Care  should  be  taken  when  a  small  sample  is  to  be  selected 
from  a  mass  of  material  to  obtain  one  which  will  be  representa- 


GRAVEL  ROADS  145 

tive  of  the  whole.  This  will  generally  involve  thoroughly  mix- 
ing the  large  mass  before  taking  a  sample  from  it.  The  sample, 
which  should  weigh  in  pounds  about  six  times  the  diameter 
in  inches  of  the  largest  holes  required,  should  be  first  dried  at 
a  temperature  of  from  100°  to  110°  C.  (212°  to  230°  F.)  to  con- 
stant weight.  The  gravel  should  then  be  separated  from  the 
sand,  clay,  or  other  fine  material  by  the  use  of  a  lo-mesh  sieve. 
The  portion  retained  on  the  sieve  should  be  passed  through 
such  of  the  following  sized  screens  as  are  required,  the  screens 
to  be  used  in  the  order  named:  3^  in.,  3  in.,  2>£  in.,  2  in., 
ij/2  in.,  i^£  m->  i  m->  -K  m->  /^  m->  and  /^  in.  The  portion 
passing  the  lo-mesh  sieve  should  be  passed  through  the  follow- 
ing sieves  in  the  order  named:  10,  20,  30,  40,  50,  80,  100, 
and  2oo-mesh  sieve.  After  the  percentages  by  weight  retained 
on  each  screen  and  each  sieve  have  been  determined,  the 
mechanical  analysis  should  be  recorded  as  follows: 

Percentage  passing  2OO-mesh         = 
Percentage  passing  loo-mesh         = 


Percentage  passing  zo-mesh 
Percentage  passing  J^-in.  screen 
Percentage  passing  ^a-in.  screen 


100.00 


Voids.  The  voids  in  a  sample  may  be  determined  in  several 
ways,  which  will  be  described  in  detail  in  Chapter  VIII. 

Quality  of  the  Stone.  The  character  of  the  stone  may  be 
determined  by  subjecting  it  to  the  standard  abrasion  and  ce- 
mentation tests  in  a  manner  similar  to  that  for  broken  stone. 
These  tests  are  described  in  Chapter  VIII  and  Appendix  III. 

CONSTRUCTION 

PREPARATION  OF  SUBGRADE.  The  subgrade  must  be  so 
prepared  that  it  offers  a  firm  surface  upon  which  to  construct 
the  gravel  crust.  It  is  brought  to  the  proper  shape  by  the  use 
of  a  road  grader  or  otherwise  and  compacted  by  rolling.  The 
transverse  slope  of  the  subgrade  may  or  may  not  be  parallel 


146  ELEMENTS   OF  HIGHWAY  ENGINEERING 

to  the  finished  surface,  since  the  gravel  surface  is  frequently 
constructed  thinner  at  the  edges  than  at  the  center  of  the  road. 
The  crown  of  a  gravel  road  is  made  from  y2  inch  to  i  inch  to 
the  foot,  2^  °f  an  mch  ^0  the  foot  being  common  practice. 

There  are  two  principal  methods  of  construction  which  will 
be  called  the  surface  method  and  the  trench  method. 

THE  SURFACE  METHOD.  In  this  method  the  gravel  is 
brought  to  the  road,  dumped  on  the  roadbed,  and  smoothed 
out  to  the  desired  shape,  the  larger  stone  being  raked  over  into 
the  bottom  of  the  crust.  A  spike-tooth  harrow  and  a  road 
drag  scraper  have  been  successfully  used  in  this  part  of  the  work. 

Width  and  Depth.  The  width  and  depth  of  the  gravel  crust 
will  depend  upon  drainage,  foundation,  and  traffic  conditions. 
A  depth  of  from  8  to  15  inches  at  the  center  is  quite  common. 
As  no  shoulders  are  built  in  the  subgrade  to  hold  back  the 
gravel,  the  edges  will  spread  out  during  compaction  so  as  to 
be  of  very  little  depth.  More  uniform  results  will  be  obtained 
if  planks  are  temporarily  laid  on  edge,  at  a  distance  apart  a 
little  less  than  the  desired  width  of  surface,  and  the  gravel  is 
filled  in  between  these  planks  to  the  required  depth. 

Compacting  the  Surface.  The  surface  is  then  rolled,  prefer- 
ably with  a  grooved  roller,  until  firmly  compacted.  A  gravel 
road  should  be  compacted  from  the  bottom  up,  but  never  with 
a  smooth  face  roller  which  has  a  tendency  to  compact  the  upper- 
most part  of  the  layer  before  the  bottom  is  consolidated.  If 
the  traffic  is  not  too  heavy  and  it  can  be  so  regulated  as  to 
travel  over  all  parts  of  the  road,  it  will  serve  to  compact  the 
gravel  much  better  than  a  smooth  face  roller.  In  order  to  take 
advantage  of  the  rolling  afforded  by  the  traffic,  the  construc- 
tion may  proceed  from  the  end  of  the  road  nearest  the  source 
of  supply  of  the  gravel.  Since  the  narrow  wheels  are  liable  to 
rut  the  surface,  a  man  should  rake  material  into  the  ruts  as 
they  are  formed  and  keep  the  whole  surface  in  as  smooth  a 
condition  as  possible.  When  the  gravel  is  deposited  in  one 
layer  the  lower  part  never  gets  the  compaction  that  it  should. 
It  is  good  practice,  therefore,  to  build  the  road  in  courses,  com- 
pacting each  course  as  it  is  laid. 


GRAVEL  ROADS  147 

Frequently  this  method  is  abused  by  simply  dumping  the 
gravel  on  the  surface,  roughly  smoothing  it  out  with  shovels, 
and  leaving  it  for  traffic  to  compact  without  giving  it  much, 
if  any,  further  attention.  Good  results  cannot  be  expected 
by  such  a  procedure. 

TRENCH  METHOD.  In  this  method  a  trench  is  constructed 
in  the  subgrade  of  the  same  width  and  depth  as  the  gravel  crust. 
On  embankments  the  distance  from  the  edge  of  the  gravel  surface 
to  the  edge  of  the  slope  of  the  bank  should  be  at  least  3  feet. 
This  part  of  the  roadbed  is  called  the  shoulder.  In  some  cases 
when  the  gravel  surface  is  deposited  in  more  than  one  course, 
the  depth  of  trench  is  made  equal  to  the  thickness  of  the  first 
course.  After  the  first  course  has  been  laid,  shoulders  are  con- 
structed at  each  side  of  the  same  depth  as  the  thickness  of  the 
remaining  courses.  The  earth  used  for  the  shoulders  must  be 
free  from  roots,  stumps,  and  other  vegetable  matter.  Material 
which  will  not  compact  properly  should  not  be  used.  The  final 
compaction  of  the  shoulders  cannot  be  accomplished  until  after 
the  gravel  surface  has  been  completed.  When  finished,  the  shoul- 
ders should  have  a  greater  slope  than  that  of  the  gravel  surface,  or 
at  least  the  same  slope,  so  that  good  surface  drainage  is  obtained 
from  the  center  of  the  road  to  the  outside  edge  of  the  shoulder. 

Constructing  the  Surface.  In  this  method  of  construction 
the  road  is  built  up  generally  in  two  courses,  although  some- 
times three  courses  are  specified.  The  number  of  courses  de- 
pends upon  the  depth  of  the  crust.  In  order  to  insure  good 
drainage  and  provide  a  stable  foundation  for  a  gravel  wearing 
course,  the  first  course  is  sometimes  constructed  of  local  broken 
stone  which  was  not  suitable  for  a  wearing  course. 

Thickness  and  Sizes  of  Gravel  j or  Courses.  From  one  to  three 
courses  are  used  in  the  trench  method  of  constructing  gravel 
roads.  The  total  thicknesses  of  the  several  courses  depend  upon 
the  traffic  and  the  nature  of  the  subgrade.  A  heavy  traffic  and 
a  soft  subgrade  will  require  the  maximum  thickness.  In  some 
cases  the  crust  is  constructed  with  a  uniform  thickness  while 
in  others  a  varying  thickness  is  employed,  the  maximum  being  at 
the  center  of  the  roadway. 


148 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


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GEAVEL   ROADS 


149 


By  reference  to  Table  2  it  will  be  noticed  -that,  in  the 
cases  cited,  the  total  thickness  of  the  gravel  crust  varies  from 
6  to  10  inches.  In  several  departments  less  gravel  is  used  at 
the  sides  than  at  the  center,  the  maximum  variation  being  10 
inches  at  the  center  and  6  inches  at  the  sides.  If  more  than 
one  grade  of  gravel  is  employed,  a  product  containing  the  smaller 


mm 

£j>>,     *      N.  '^  L-  ^ 


FIG.  57. 


Lower  Course  of  a  Gravel  Road  Before  Being  Filled  with  Fine 
Material. 


particles  is  used  in  the  wearing  course.  Whereas  considerable 
variation  exists  relative  to  the  maximum  size  to  employ  in  the 
lower  course,  see  Fig.  57,  it  has  generally  been  found  most 
satisfactory  to  use  a  product  which  will  pass  through  a  i*^- 
inch  screen  for  the  wearing  course.  The  sizes  employed  are 
governed  by  the  character  of  the  local  supplies  of  gravel,  the 
thicknesses  of  courses,  and  the  requisites  of  gravel  mentioned 
at  the  beginning  of  this  chapter.  The  above  statements  are 
well  illustrated  by  the  requirements  of  the  1915  Maine  State 
Highway  Commission  specifications  which  state  that:  "Two- 
Course  Road:  Whenever  the  smaller  sizes  of  stone  predomi- 
nate, the  bottom  course  shall  have  a  thickness  of  four  inches 
after  rolling.  This  course  shall  be  bonded  with  fine  material 
before  the  second  course  is  applied.  The  second,  or  top  course, 


150  ELEMENTS   OF  HIGHWAY  ENGINEERING 

shall  be  similar  to  the  bottom  course  and  shall  have  the  same 
thickness.  It  shall  be  bonded  with  fine  material  until  a  firm, 
hard,  smooth  surface  is  produced.  Three-Course  Road :  When- 
ever the  larger  sizes  of  stone  predominate,  the  bottom  course 
shall  have  a  thickness  of  three  inches  after  rolling.  The  second 
course  shall  be  of  the  same  kind  of  material  and  of  the  same 
thickness.  The  top  course  shall  have  a  thickness  of  two  inches 
after  rolling  and  contain  stone  not  larger  than  one  and  one-half 
inches  in  size.  Each  course  shall  be  thoroughly  bonded  with 
fine  material  by  mixing,  rolling,  and  sprinkling  until  a  firm, 
hard,  smooth  surface  is  produced."  Practice,  dependent  upon 
economic  considerations  and  personal  views,  varies  to  a  large 
extent  relative  to  the  above  elements  of  gravel  road  construction. 

The  proper  depths  of  the  various  courses  during  construction 
can  be  maintained  by  lines  stretched  between  stakes,  or  by 
blocks  placed  on  the  surface  and  the  material  levelled  off  to 
the  tops  of  the  blocks. 

Cross-Sections.  A  typical  cross-section  of  a  two-course  road 
is  shown  in  Fig.  58,  which  is  the  standard  section  of  the  Maine 
State  Highway  Department. 

Screening  Gravel.  As  it  is  frequently  impossible  to  find  a 
gravel  that  contains  the  exact  proportions  of  sizes  desired,  it  is 
necessary  to  screen  out  some  of  the  large  or  fine  material. 
Screening  may  be  accomplished  by  hand  or  by  machine.  In 
screening  with  machinery  a  bucket  elevator  can  be  erected  so 


FIG.  58.     Cross-Section  Gravel  Road.     Maine  State  Highway  Department. 

as  to  dump  the  gravel  onto  a  chute  screen  or  a  rotary  screen, 
the  screened  output  falling  into  bins  constructed  high  enough 
so  that  wagons  can  be  filled  underneath  the  pockets.  The 
gravel  to  be  screened  can  be  brought  to  the  boot  of  the  elevator 


GRAVEL  ROADS  151 

by  wagon,  drag  or  wheel  scraper.  Frequently  in  gravel  banks 
containing  strata  of  different  sizes  of  gravel,  it  is  practicable 
to  avoid  screening  by  careful  excavation  of  the  several  sizes 
required  for  the  different  courses. 

Spreading  the  Gravel.  The  gravel  for  each  course  as  it  is 
brought  to  the  road  is  either  dumped  to  one  side  of  the  road- 
bed and  shovelled  into  place  or  is  shovelled  directly  from  the 
wagon  into  place.  The  gravel  may  also  be  spread  directly  on 
the  roadbed  when  bottom  dump-wagons  are  used;  otherwise  a 
dumping  board  should  be  used  if  it  is  necessary  to  dump  the 
gravel  on  the  roadbed.  The  gravel  is  shaped  up  by  using  either 
shovels  and  rakes  or  a  tooth  harrow  and  a  road  grader.  When 
machines  are  used  a  considerable  length  of  gravel  should  be 
placed  before  shaping  with  the  machines,  as  otherwise  their 
use  would  not  be  economical. 

Compacting  the  Gravel.  Each  course,  after  it  has  been  shaped 
up,  is  thoroughly  compacted  with  a  roller,  both  horse-drawn 
and  power-driven  rollers  being  employed.  Sectional  rollers, 
weighing  about  1000  pounds  per  foot  of  width,  are  very  satis- 
factory for  the  compaction  of  gravel.  The  sheep's  foot  roller 
has  also  been  successfully  employed.  Some  engineers  do  not 
favor  the  use  of  the  heaviest  types  of.  rollers.  Rolling  for  each 
course  should  be  continued  until  a  firm  and  even  surface  is 
obtained.  If  any  depressions  occur  during  the  rolling,  they 
should  be  filled  up  with  the  same  size  of  material  as  is  used  in  the 
course  being  constructed.  The  top  course  is  usually  puddled 
with  water  during  the  process  of  rolling.  The  water  when  mixed 
with  the  binder  causes  it  to  produce  cement-like  qualities.  Too 
much  water,  however,  is  detrimental,  as  it  tends  to  wash  out 
some  of  the  finer  binding  material  and  to  soften  the  subgrade. 
Rolling  should  always  progress  from  the  sides  toward  the 
center  so  as  to  maintain  the  crown  of  the  road.  Ultimately 
the  rolling  should  extend  over  the  whole  width  of  road,  in- 
cluding the  shoulders.  Gravel  will  compact  to  about  80  per- 
cent of  its  depth,  loose  measure.  Hence,  if  a  finished  thickness 
of  8  inches  is  desired,  it  will  be  necessary  to  use  a  total  depth 
of  10  inches  loose  measure  in  the  various  courses. 


152 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


Cost  Data.  The  cost  per  square  yard  of  gravel  roads  usually 
varies  from  30  to  80  cents  for  thicknesses  of  from  5  to  10  inches. 
In  the  following  table  are  given,  for  several  localities  through- 
out America,  prices  of  gravel  roads  constructed  with  different 
thicknesses  of  gravel. 

From  Municipal  Engineering,  June,   1915 


City 

Square 
Yards 

Price  per 
Square  Yard 

Total 
Thickness  of 
Gravel  Crust 
in  Inches 

Lowell,  Mass  

82,IOO 

$0.20 

6 

Rutland   Vt 

24  "*OO 

O   2S 

6 

Ocean  City,  N.  J 

IO  OOO 

O   27 

8 

Richmond,  Ind  . 

2T>  2OO 

o  40 

c 

Flint,  Mich 

^0,855 

O   7T> 

1  1 

Appleton,  Wis 

45.OOO 

O   ^5 

1  1 

Bellingham,  Wash 

20,562 

o  40 

0 

Lake  Charles,  La  . 

Q.OOO 

O   ^6 

\y* 

Clarksdale,  Miss.  .                                  .  .  .  . 

2,800 

O.6o 

9 

Longview,  Texas  

3,180 

0-55 

8 

MAINTENANCE 

It  may  take  several  months  before  a  gravel  crust  is  thor- 
oughly compacted,  no  matter  how  well  it  may  have  been  rolled 
during  construction.  During  this  period  careful  attention 
should  be  given  to  the  road,  and  the  ruts  and  hollows  should 
be  patched  as  soon  as  they  are  formed.  In  times  of  wet  weather 
or  of  frost  a  gravel  surface  will  be  soft  and  rut  very  easily. 
As  in  the  case  of  earth  roads,  the  road  drag  is  one  of  the  best 
machines  with  which  to  maintain  a  gravel  road.  Where  a  road 
grader  would  unnecessarily  disturb  the  surface,  the  road  drag 
serves  to  simply  smooth  up  the  road,  fill  in  the  hollows,  and 
push  just  enough  of  the  material  toward  the  center  to  maintain 
the  crown.  Dragging  will  be  required  more  frequently  for  the 
first  year  after  the  road  is  completed  than  at  any  other  time. 
As  is  the  case  in  all  road  dragging,  the  work  should  be  done 
when  the  surface  is  in  a  moist  and  soft  condition.  As  the  road 
ages  and  becomes  set,  the  road  drags  will  not  have  any  effect 
unless  a  prolonged  period  of  rain  has  made  the  road  very  soft. 


GRAVEL  ROADS  153 

There  are  many  miles  of  gravel  roads  that  have  .been  main- 
tained by  means  of  a  road  drag  at  a  cost  of  from  $5  to  $10  per 
year  per  mile. 

All  patching  should  be  done  when  the  road  is  in  a  wet 
condition,  as  the  new  material  added  will  bond  to  the  old 
and  compact  much  better  than  when  in  a  dry  state.  Great 
care  should  be  taken  not  to  get  the  patches  too  high,  as 
such  a  procedure  is  liable  to  create  a  new  hollow  just  be- 
yond the  one  patched.  As  near  the  same  size  and  kind  of 
material  should  be  used  in  making  the  patches  as  was  used  in 
building  the  course.  Constant  patching  and  intelligent  work 
with  the  road  drag  serves  to  keep  a  gravel  road  in  good  pass- 
able condition  until  it  is  entirely  worn  out  and  requires 
resurfacing. 

When  resurfacing  is  necessary,  the  new  gravel  is  added  in  a 
manner  similar  to  new  construction.  As  in  patchwork,  best 
results  will  be  obtained  by  resurfacing  when  the  old  road  is  in 
a  soft  condition. 

An  essential  part  of  the  maintenance  work  is  to  keep  ditches, 
drains,  and  culverts  clear  to  provide  for  the  removal  of  the 
water  which  falls  onto  the  road. 


CHAPTER  VIII 
BROKEN  STONE  ROADS 

Broken  stone  roads  are  extensively  built  in  all  countries 
where  stone  is  available.  Although  the  water-bound  broken 
stone  road  can  no  longer  be  built  and  maintained  at  a  reason- 
able expense  when  subjected  to  certain  types  of  traffic,  there 
are  many  conditions  under  which  it  will  continue  to  prove  the 
most  economical  type  of  surfacing.  The  conclusion  of  the  Second 
International  Road  Congress  (1910)  with  regard  to  the  use  of 
the  water-bound  type  of  broken  stone  road  in  municipalities 
was  as  follows:  "Macadam  constructed  according  to  the  methods 
of  Tresaguet  and  McAdam  causes  dust  and  mud,  is  expensive 
to  maintain,  and  is  only  suitable  in  large  cities  for  streets  where 
the  traffic  is  not  very  great  or  heavy." 

ROCKS 

ROCK  CLASSIFICATION.  Rocks  may  be  separated  into  the 
following  classes: 

1.  Igneous   rocks,  or    those   which   have  been   formed    by 
mineral  matter   flowing   upward   in   a  molten   condition   and 
cooling  near  the  surface. 

2.  Aqueous  rocks,  or  those  formed  through  the  agency  of 
water,  including  all  sedimentary  rocks. 

3.  Metamorphic  rocks,  or  those  rocks  changed  by  dynamic 
or  chemical  agencies  from  their  original  condition. 

Some  rocks  may  be  identified  with  the  unaided  eye  by  noting 
the  color,  structure,  weight,  and  hardness.  By  preparing  micro- 
scopic slides  and  examining  them  under  a  petrographical  micro- 
scope, it  is  possible  to  identify  those  which  cannot  be  determined 
by  the  eye  alone. 

Definitions.  Terms  pertaining  to  rocks  are  described  in 
the  following  definitions. 

154 


BROKEN  STONE   ROADS  155 

A  morphous.    A  textural  term  used  to  describe  a  rock  structure 
without  definite  form  or  crystalline  composition. 

Cellular.     A  textural  term  used  to  describe  a  rock  structure 
containing  cells  due  to  weathering  out  of  some  constituent. 

Colloidal.     A  textural  term  used  to  describe  a  jelly  or  glue- 
like  rock  structure. 

Crystalline.    A  textural  term  used  to  describe  a  rock  struc- 
ture similar  to  that  of  granite 

Foliated.    A  textural  term  used  to  describe  a  rock  structure 
which  has  a  tendency  to  split  along  lines  of  stratification. 

Glass.     A  textural  term  used  to  describe  an  amorphous  rock 
structure  formed  by  the  quick  chilling  of  a  fused  lava. 

Granitoid.     A  textural  term  used  to  describe  those  igneous 
rocks  which  are  entirely  composed  of  recognizable  minerals. 

Granular.    A  textural  term  used  to  describe  a  rock  structure 
made  up  of  distinct  grains. 

Holy  crystalline.  A  textural  term  used  to  describe  a  rock 
structure  that  consists  entirely  of  crystallized  minerals. 

Laminated.  A  textural  term  used  to  describe  a  banded  struc- 
ture which  is  characteristic  of  many  sedimentary  rocks. 

Massive.  A  textural  term  used  to  describe  igneous  rocks  that 
show  no  stratification. 

Plutonic  Rocks.  Rocks  which  were  formed  by  the  cooling 
01  molten  mineral  matter  before  it  reached  the  surface. 

Porphyritic.  A  textural  term  used  to  describe  a  compact 
structure  throughout  which  there  are  large  crystals. 

Schistose.  A  textural  term  used  to  describe  a  rock  structure 
which  has  a  tendency  to  split  along  lines  of  stratification. 

Stratified.  A  textural  term  used  to  describe  a  rock  structure 
composed  of  parallel  layers. 

Volcanic  Rocks.  Rocks  which  have  been  formed  by  mineral 
matter  erupted  in  a  molten  condition  and  cooled  on  the  surface. 

Mineral  Constituents.  A  rock  is  a  mineral  or  combination 
of  minerals.  There  are  a  few  rocks  which  are  composed  en- 
tirely of  one  mineral,  but  the  majority  are  made  up  of  a 
combination  of  two  or  more  minerals.  Among  the  most 
important  chemical  compounds  occurring  in  rocks  are  silicates, 


156  ELEMENTS   OF  HIGHWAY   ENGINEERING 

oxides,  carbonates,  sulphates,  chlorides,  phosphates,  sulphides, 
and  one  native  element,  graphite.  Sedimentary  rocks  are  spoken 
of  as  calcareous,  siliceous,  ferrugineous,  or  argillaceous  according 
as  lime,  silica,  iron  oxides,  or  clayey  matter  predominates.  Erup- 
tive rocks  are  spoken  of  as  acidic  or  basic,  the  former  being  those 
showing  more  than  65  percent  silica,  and  the  latter  those  which 
show  less  than  55  percent,  but  are  rich  in  iron,  lime,  and  mag- 
nesian  constituents.  Among  the  more  common  minerals  found 
in  rocks  are  the  following:  quartz,  orthoclase,  plagioclase,  micro- 
cline,  augite,  hornblende,  biotite,  muscovite,  garnet,  kaoline,  hy- 
persthene,  olivine,  epidote,  calcite,  dolomite,  magnetite,  chlorite, 
and  serpentine. 

The  mineral  constituents  which  make  up  a  rock  can  be 
determined  by  means  of  the  crystalline  formation,  by  chemical 
analysis,  by  blow-pipe  analysis,  and  by  microscopical  examination. 

Table  No.  3*  gives  the  essential  and  important  mineral 
constituents  used  in  highway  construction.  Group  i  to  8  com- 
prises the  plu tonic  igneous  rocks,  9  to  14  the  volcanic  igneous, 
15  to  20  the  sedimentary,  and  21  to  34  the  metamorphic  rocks 
or  crystalline  schists. 

Trap.  The  term  trap  has  been  denned  by  Kemp  as  a  useful 
field  name  for  any  dark,  finely  crystalline  igneous  rock.  The 
characteristics  of  the  principal  rocks  usually  included  under  the 
name  of  trap  are  as  follows.  Andesites  are  generally  gray, 
greenish,  or  reddish  in  color.  Their  structure  when  examined 
under  a  microscope  is  found  to  vary  from  glassy  to  holocrystal- 
line.  Their  principal  constituent  is  plagioclase.  Basalts  are 
homogeneous  rocks,  generally  of  a  dark  gray  or  black  color, 
although  red  and  brown  colors  are  also  common.  In  structure 
they  vary  from  glassy  to  holocrystalline.  Diabases  are  holo- 
crystalline  in  structure  and  vary  in  color  from  green  to  a  dark 
gray  or  black.  (See  Fig.  59.)  Peridotite  is  greenish  or  black 
in  color  with  a  variable  structure  that  may  be  either  crystalline, 
granular,  or  porphyritic. 

Diorite.     The  diorites  are  granitoid  rocks  whose  essential 

*From  Table  in  "Rocks  for  Road   Making,"  by  E.  C.  E.  Lord,  U.  S. 
Office  of  Public  Roads  Bulletin,  No.  31. 


BROKEN  STONE   ROADS 


157 


constituents  are  plagioclase,  feldspar,  either  labradorite  or  oligo- 
clase,  and  hornblende  or  biotite.  They  are  green,  dark  gray,  or 
black  in  color.  Gabbros  are  crystalline  granular  in  structure, 


Diabase. 


Granite. 


Courtesy  of  the  Department  of  Geology  in  Columbia  University. 

Quartzite.  Mica-Schist. 

FIG.  59.      Microstructure  of  Four  Rocks  Used  as  Highway  Materials. 

the  prevailing  color  being  black  green.    Its  principal  constituents 
are  plagioclase,  augite,  and  hornblende. 

Granite.     The  essential  constituents  of  granite  are  quartz, 
orthoclase,  and  plagioclase,  combined  usually  with  mica,  horn- 


158 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


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BROKEN  STONE   ROADS  159 

blende,  and  pyroxene.  It  is  holocrystalline  granular  tn  structure. 
(See  Fig.  59.)  It  may  be  gray,  green,  yellow,  or  red  in  color, 
the  lighter  colors  being  due  to  the  feldspar  and  the  darker  col- 
ors due  to  the  mica  and  hornblende.  Quartz  porphyries  have 
the  same  constituents  as  granite  but  are  porphyritic  in  structure, 
having  quartz  crystals  scattered  through  a  ground  mass  which 
may  be  red,  gray,  yellow,  green,  black,  or  white  in  color. 

Syenite.  Syenites  are  of  the  same  composition  as  granites 
except  that  they  contain  no  quartz.  In  structure  and  color 
they  are  the  same  as  granite. 

Gneiss.  Gneisses  are  of  a  holocrystalline  granular  structure 
arranged  in  parallel  bands.  Gneisses  are  practically  the  same 
in  composition  and  color  as  the  granites,  the  principal  differ- 
ence being  in  the  structure.  The  different  varieties,  as  in 
granites,  are  called  by  the  name  ,  of  the  predominating 
mineral. 

Limestone.  Limestones  are  extremely  variable  in  both  color 
and  structure.  All  shades  from  white  through  a  gray  to  a  black 
are  common,  and  sometimes  even  red  and  yellow  are  found. 
They  are  stratified  in  structure .  and  vary  from  a  soft  variety 
to  a  rock  with  a  dense  structure  that  breaks  with  a  distinct 
fracture.  Chats,  a  dolomitic  limestone,  is  a  term  used  in  the 
West  to  denote  the  tailings  of  lead  mines. 

Sandstone.  Sandstones,  like  limestones,  are  variable  both 
as  to  color  and  structure.  In  color  they  are  red,  brown,  green, 
and  yellow.  Pudding  stone  or  conglomerate  is  a  coarse  sand- 
stone. Breccia  is  similar  to  conglomerate  except  that  the  stones 
are  more  angular.  Flints,  so-called  in  Great  Britain,  are  found 
in  the  upper  layers  of  chalk-pits  or  in  gravel  deposits  near  the 
chalk  areas.  They  are  made  up  of  colloidal  and  crystalline 
silica.  Chert  is  a  variety  of  quartz  having  a  flinty  structure. 
Quartzites  are  metamorphosed  sandstones,  being  brown,  red,  or 
green  in  color.  (See  Fig.  59.) 

Schist.  The  schists  differ  from  the  gneisses  principally  in 
the  absence  of  feldspar.  Amphibolite  has  hornblende  for  its 
principal  constituent  and  is  a  tough  and  often  a  massive  rock. 
(See  Fig.  59.) 


160  ELEMENTS   OF   HIGHWAY  ENGINEERING 

Slate.  Slate  is  an  indurated  or  hardened  clay  having  a 
foliated  structure  and  generally  dark  in  color. 

Fieldstone.  Fields  tones  are  boulders  which  have  been  car- 
ried along  by  glaciers  and  are  found  mainly  in  those  districts 
which  were  covered  by  great  ice  sheets.  They  are  composed  of 
a  variety  of  different  kinds  of  rocks. 

PROPERTIES  ROCK  SHOULD  POSSESS.  A  rock  should  possess 
the  following  characteristics  in  order  to  make  a  first-class  stone 
for  water-bound  broken  stone  roads:  It  should  be  tough  so  as 
to  resist  the  shocks  from  the  traffic;  it  should  have  a  good 
resistance  to  the  wear  caused  by  the  grinding  action  of  wheels; 
it  should  possess  good  cementing  power;  it  should  break  with 
a  clean  angular  fracture.  The  various  rocks  used  for  building 
highways  are  popularly  known  as  trap,  granite,  limestone,  sand- 
stone, and  fields  tones. 

Trap.  Trap  rocks  are  extremely  hard  and  tough  and  their 
excellent  wearing  and  binding  qualities  have  caused  their  wide- 
spread use  throughout  those  sections  of  the  country  where  they 
are  found.  When  used  in  the  construction  of  broken  stone 
roads  subjected  to  a  light  traffic,  however,  the  wear  on  the 
stones  will  not  usually  be  sufficient  to  make  enough  binder  to 
hold  the  stones  together. 

Granite.  Granites,  which  have  a  close,  even,  and  granular 
structure,  make  good  road  material  for  broken  stone  roads  which 
take  a  light  traffic.  If  of  a  coarse  structure  they  are  not  so 
desirable,  but  may  be  used  in  the  foundation  courses. 

Limestone.  Limestones  possess  excellent  binding  qualities 
but  are  generally  neither  hard  nor  tough  and  therefore  are  only 
suitable  for  roads  having  a  light  traffic. 

Sandstone.  Sandstones,  due  to  the  fact  that  they  are  easily 
broken  up  under  the  action  of  traffic  and  are  usually  lacking  in 
binding  qualities,  are  generally  not  considered  as  good  road 
material  except  for  the  foundation  courses.  Quartzites,  which 
are  metamorphosed  sandstones,  give  better  results  than  sand- 
stones. 

Fieldstones.  Fieldstones  frequently  make  a  satisfactory  ma- 
terial for  light  traffic  roads.  They  are  extremely  variable  in 


BROKEN  STONE   ROADS 


161 


composition  and  hence  wearing  courses  composed  erf  them  may 
wear  unevenly. 

Testing  the  Rock.     In  order  to  ascertain  the  value  of  any 
rock  as  a  material  suit- 
able  for  highway  build-  , 

ing,  there  are  several 
tests  that  have  been 
developed  which  give 
some  indication  as  to 
what  may  be  expected 
of  a  rock  when  used  in 
the  road.  The  tests  are 
made  to  determine  cer- 
tain specific  character- 
istics, and  although  the 
results  of  the  tests  do 
not  always  agree  with 
the  results  obtained  in 
service  tests,  still  they 
are  a  great  aid  in  com- 
paring the  respective 
qualities  of  different 
stones.  There  are  many 
variable  conditions  to 
which  a  road  is  sub- 
jected, and  since  it  is 
difficult  to  duplicate 
these  conditions  by  any 
accelerated  mechanical 
test,  the  best  knowledge 
in  regard  to  the  worth 
of  any  rock  will  be  ob- 
tained from  observations 
of  its  wear  in  actual 
service.  Tests  are  made 
to  determine  the  phys- 
ical properties  of  abra- 


•• 


162  ELEMENTS   OF  HIGHWAY  ENGINEERING 

sion,  cementing  value,  toughness,  hardness,  absorption,  and 
specific  gravity.  Detailed  descriptions  of  the  methods  of 
making  the  tests  have  been  included  in  Appendix  III.  The 
relative  values  of  the  results  of  tests  as  listed  in  the  following 
descriptions  are  those  proposed  by  the  U.  S.  Office  of  Public 
Roads. 

Abrasion.  This  test  is  made  by  means  of  the  Deval  machine. 
This  machine,  Fig.  60,  consists  of  a  series  of  cylinders  or  tubs 
mounted  on  a  shaft  with  the  long  axes  of  the  tubs  making  angles 
of  30  degrees  with  the  horizontal.  Mounting  the  cylinders  in  this 
manner  causes  the  rock  to  be  thrown  from  one  end  of  the  cylinders 
to  the  other  as  the  machine  revolves.  The  rock  to  be  tested  is 
broken  in  nearly  uniform  pieces,  about  fifty  pieces  weighing 
approximately  5  kilograms  constituting  a  test  sample.  Ten 
thousand  revolutions  of  the  tubs  constitute  a  test.  The  mate- 
rial worn  off  which  will  pass  through  a  /{6-inch  mesh  sieve  is 
considered  the  amount  of  wear.  This  may  be  expressed  either  as 
the  percent  of  the  5  kilograms  used  in  the  test,  or  the  French  co- 


efficient may  be  given;  that  is,  coefficient  of  wear  20  X       = 

W  is  the  weight  in  grams  of  the  detritus  under  /{6  inch  in  size 
per  kilogram  of  rock  used.  A  French  coefficient  of  wear  of  8  is 
low,  8  to  13  medium,  14  to  20  high,  and  above  20  very  high. 

Cementing  Value.  The  test  for  cementing  value  as  made  by 
the  U.  S.  Office  of  Public  Roads  is  as  follows:  Five  hundred 
grams  of  the  rock  to  be  tested,  broken  to  pass  a  X-inch  rnesh 
sieve,  are  ground  in  a  ball  mill.  The  addition  of  water  in  the 
ball  mill  makes  the  charge  into  an  extremely  stiff  dough.  This 
dough  is  removed  and  placed  in  a  metal  die,  25  millimeters  in 
diameter,  and  subjected  to  pressure  in  a  hydraulic  press.  The 
cylindrical  briquette,  25  millimeters  in  height,  is  placed  in  the 
machine  used  for  testing  the  briquette,  shown  in  Fig.  61.  In 
this  machine  a  i  -kilogram  hammer  is  raised  by  a  revolving  cam 
to  a  height  of  i  centimeter.  The  hammer  falls  on  a  plunger 
and  transmits  the  energy  of  its  blow  through  the  plunger  to 
the  test  piece.  The  instrument  is  provided  with  a  self-recording 


Courtesy  of  the  U.  S.  Office  of  Public  Roads. 

FIG.  61.     Impact  Machine  for  Determining  Cementing  Value. 


164  ELEMENTS    OF   HIGHWAY   ENGINEERING 

apparatus  which  registers  each  blow  struck  until  the  test  piece 
fails.  The  average  of  the  number  of  blows  on  5  briquettes  is 
taken  as  a  result  of  the  test.  A  result  of  10  is  low,  10  to  25 
fair,  26  to  75  good,  76  to  100  very  good,  over  100  excellent. 

Toughness.  The  test  for  toughness  is  made  in  the  machine 
shown  in  Fig.  62.  The  usual  test  piece  consists  of  a  cylinder, 
25  millimeters  in  diameter,  and  25  millimeters  in  height,  cut 
perpendicular  to  the  cleavage  of  the  rock.  The  test  consists  of 
a  i -centimeter  fall  of  a  hammer  weighing  2  kilograms  for  the 
first  blow,  and  an  increased  fall  of  i  centimeter  for  each  suc- 
ceeding blow  until  failure  of  the  test  piece  occurs.  The  number 
of  blows  necessary  to  destroy  the  test  piece  is  used  to  represent 
the  toughness.  A  result  of  13  is  low,  13  to  19  medium,  and 
above  19  high. 

Hardness.  The  test  for  hardness  is  made  by  means  of  a 
Dorry  machine,  Fig.  63,  which  consists  of  a  revolving  steel  disk 
on  which  is  fed  a  standard  quartz  sand,  the  grains  of  which  pass 
a  30-  and  are  retained  on  a  40-mesh  sieve.  A  rock  core,  25 
millimeters,  is  cut  from  the  rock  and  its  faces  ground  off  level. 
Two  cores  are  used  in  each  test  and  are  placed  in  the  dies, 
which  are  supported  by  the  guide  cylinders  shown  near  the 
funnels.  The  test  piece  is  first  weighed  and  is  then  ground  on 
one  face  for  1,000  revolutions,  after  which  it  is  reversed  and 
the  other  face  ground  for  the  same  number  of  revolutions.  The 
loss  in  weight  of  the  specimen  is  determined  at  the  end  of  each 
1,000  revolutions,  and  the  average  loss  in  weight  is  used  in 
stating  the  hardness  of  the  rock,  which  is  expressed  by  the 
formula,  Hardness  =  20  —  y£  W,  where  W  =  loss  in  grams 
per  1,000  revolutions.  Rocks  having  a  coefficient  of  hardness 
below  14  are  called  soft,  from  14  to  17  medium,  above  17  hard. 

Absorption.  The  amount  of  water  absorbed  by  a  rock  is 
generally  expressed  as  the  number  of  pounds  of  water  absorbed 
per  cubic  foot. 

Specific  Gravity.  The  specific  gravity  of  rock  is  determined 
by  the  displacement  in  water  method.  The  specific  gravity  of 
rock  screenings  is  determined  by  means  of  the  Jackson  apparatus. 

Results    of    Tests.     The    average    results    of    the    abrasion, 


Courtesy  of  the  U.  S.  Office  of  Public  Roads. 

FIG.  62.     Page  Impact  Machine  for  Determining  Toughness. 


Courtesy  of  the  U.  S.  Office  of  Public  Roads. 

FlG.  63.     Dorry  Machine. 


BROKEN  STONE   ROADS 


167 


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168  ELEMENTS    OF   HIGHWAY  ENGINEERING 

cementing  power,  toughness,  and  hardness  for  the  principal  rocks 
used  in  road  building  are  given  in  Table  No.  4,  compiled  by 
the  U.  S.  Office  of  Public  Roads  and  Rural  Engineering. 

QUARRYING  AND  CRUSHING 

STRIPPING  THE  QUARRY.  Before  any  drilling  is  commenced 
in  a  rock  quarry,  it  is  necessary  to  clean  off  all  dirt  and  disin- 
tegrated material  from  the  rock  surface.  This  is  called  stripping 
the  quarry.  Frequently  the  ledge  is  exposed  so  that  there  is 
very  little  of  this  work  to  be  done.  If  stripping  is  not  accom- 
plished in  a  thorough  manner  and  kept  well  ahead  of  the  drilling 
and  blasting  operations,  there  will  always  be  trouble  caused  by 
this  dirty  material  being  mixed  with  the  stone. 

DRILLING.  Drilling  is  accomplished  with  hammer  drills, 
churn  drills,  and  power  drills. 

Hammer  Drills.  For  quarrying  purposes  a  hammer  drill  is 
usually  held  by  one  man  and  struck  by  two  others  with  ham- 
mers. Holes  in  small  boulders  may  be  drilled  by  the  same  man 
both  holding  and  striking  the  drill. 

Churn  Drills.  A  churn  drill  is  operated  by  one  or  more 
men,  depending  upon  its  weight.  In  operating  a  churn  drill 
the  man  or  men  raise  the  drill  and  allow  it  to  drop  on  the  rock, 
giving  it  a  slight  turn  between  blows. 

Power  Drills.  Power  drills  are  operated  by  steam,  air,  and 
electricity.  In  all  of  these  types  the  drill  is  given  a  reciprocating 
motion,  striking  many  short  stroke  blows  to  the  minute  against 
the  rock  face.  Between  each  blow  the  drill  bit  is  given  a  partial  turn. 
The  drills  are  generally  mounted  on  tripods  as  shown  in  Fig.  64. 

Cost  of  Drilling.  The  cost  and  speed  of  drilling  depend  upon 
the  kind  of  rock,  the  size  of  hole,  and  the  depth  of  hole  drilled. 

Gillette  gives  the  following  as  the  speed  and  cost  of  hammer 
drilling  holes  6  feet  deep: 


Feet  in 
10  Hours 

Cost  per 
Foot,  Cts. 

Granite 

7 

75 

Trap  (basalt)                                                          .            ... 

II 

48 

Limestone                                    

16 

33 

BROKEN  STONE   ROADS 


169 


Power  drills  may  be  obtained  to  drill  practically  any  size  of 
hole  from  ^  of  an  inch  to  3  inches  in  diameter.  As  would  be 
expected,  these  drills  are  capable  of  drilling  at  a  much  more 


fc  /,  "4; 
Courtesy  of  the  Ingersoll,  Rand  Co. 


FIG.  64.     Steam  Drill. 


rapid  rate  than  either  hammer  or  churn  drills.  From  about 
35  to  75  feet  per  lo-hour  day  can  be  accomplished  with  a  power 
drill,  the  rate  depending  principally  upon  the  kind  of  rock  and 
the  number  of  set-ups  that  have  to  be  made. 


170 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


BLASTING.  The  explosives  used  in  blasting  are  powder  and 
dynamite.  Gunpowder  is  a  combination  of  saltpetre,  sulphur, 
and  charcoal,  saltpetre  being  the  principal  constituent.  It  is 
exploded  by  ignition  and  in  doing  so  develops  gases  amounting 
to  almost  three  hundred  times  its  original  volume.  Dynamite 
is  a  mixture  of  nitroglycerine  with  an  absorbent  material.  Dyna- 
mite has  about  four  times  the  same  explosive  force  as  powder. 
Dynamite  does  not  explode  by  ignition,  but  by  percussion.  A 


FIG.  65.     Breaking  Stone  with  Hand  Tools. 

fuse  is  used  to  explode  powder.  To  explode  dynamite  a  similar 
fuse  is  used  which  explodes  a  cap.  The  cap  is  placed  in  one  of 
the  sticks  of  dynamite  constituting  the  charge,  and  the  percus- 
sion of  the  cap  explodes  the  dynamite.  Instead  of  using  a  powder 
fuse,  dynamite  is  often  exploded  by  means  of  an  electric  battery. 
By  this  method  several  charges  of  dynamite  can  be  set  off  simul- 
taneously. Prelini  states  that  the  energy,  released  by  setting 
off  an  explosive,  is  exerted  in  all  directions  or  in  the  form  of  a 
sphere,  the  energy  decreasing  from  the  center  towards  the  sur- 
face. Blasting  alone  may  break  up  certain  kinds  of  rocks  so 
that  very  little  sledging  is  necessary  to  make  the  rock  of  a  size 
suitable  to  put  through  a  crusher.  Ordinarily,  however,  the 
pieces  have  to  be  broken  up  by  hand  into  smaller  sizes.  The 


BROKEN  STONE   ROADS 


171 


openings  of  a  jaw  crusher  of  common  size  is  about  8  by  16  inches. 
When  fieldstones  are  used,  the  boulders  are  often  of  such  a  size 
that  only  sledging  is  necessary  to  make  them  suitable  for  crushing. 
CRUSHING  PLANTS.  In  the  early  days  of  road  construction, 
the  stone  was  broken  by  hand.  (See  Fig.  65.)  Throughout  the 


Courtesy  oftne  Austin  Mfg.  Co. 

FIG.  66.     Gyratory  Crusher. 

United  States  mechanical  crushers  are  now  used  for  the  manu- 
facture of  broken  stone.  A  complete  crushing  plant  for  road- 
building  purposes  consists  of  a  boiler,  engine,  crusher,  elevator, 
screen,  and  storage  bins. 

Crushers.     The  crushers  are  of  two  distinct  types;   namely, 
the  gyratory  and  the  jaw  crushers.     Both  types  of  crushers 


172 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


have  some  means  of  regulating  the  openings  so  that  by  using 
the  proper  opening  together  with  appropriate  crushing  plates, 
almost  any  size  of  crushed  product  may  be  obtained.  The  size 
of  the  crushed  product  is  limited  by  the  smallest  opening  be- 
tween the  jaws  at  the  outlet  end.  The  gyratory  crusher  is  a 
more  recent  invention  than  the  jaw  crusher.  That  the  gyratory 


Courtesy  of  the  Good  Rouds  \lachinery  Co. 

FIG.  67.     Jaw  Crusher,  Sectional  View. 

crusher  produces  a  more  uniform  product  and  is  a  more  dur- 
able machine  are  the  main  advantages  claimed  for  it  over  the 
jaw  crusher.  With  the  same  horse-power,  this  type  of  crusher 
will  generally  produce  a  larger  output.  The  type  and  size  of 
crusher  to  be  used  depend  upon  the  nature  of  the  rock  to  be 
crushed,  the  size  of  the  product  desired,  and  the  type  of  plant, 
that  is,  permanent  or  portable. 

Gyratory  Crushers.  The  gyratory  crusher,  see  Fig.  66,  is 
extensively  used  for  permanent  plants.  Its  great  weight  and 
height  have  not  made  it  generally  adaptable  for  portable  plants, 
although  it  is  sometimes  made  for  this  purpose. 

Jaw  Crushers.    Jaw  crushers  are  largely  used  for  portable 


BROKEN   STONE   ROADS 


173 


crushers.  Fig.  67  shows  a  sectional  view  of  this  type.  They 
are  designated  by  the  size  of  the  jaw  openings  at  the  top.  The 
size  of  8  by  1 6  inches  is  very  commonly  used. 

Boilers  and  Engines.  The  crushers  may  be  run  by  gasoline- 
engines  or  by  steam-engines,  the  latter  being  perhaps  more 
common.  The  steam-engine  is  generally  mounted  upon  a  hori- 
zontal boiler  which  is  in  turn  placed  on  wheels  so  that  it  can  be 
easily  transported  from  place  to  place. 

Elevators  and  Screens.  The  stone  as  it  comes  from  the 
crusher  is  carried  by  means  of  a  bucket  elevator  to  the  revolving 


r"  v"  *»  '  ••* '     ' .  /1Lt-_ V"j  *V  *1  •?*.  »*  ^<f*^\* 


FIG.  68.     Rotary  Screen. 

screen  which  is  located  over  the  bin.  Fig.  68  shows  a  rotary 
screen  equipped  with  a  dust  jacket.  In  portable  plants  the 
arrangement  of  the  elevator,  the  screen,  and  the  bins  is  such 
that  they  can  be  readily  dismantled  for  transportation  purposes. 
The  elevators  and  screens  are  made  in  standard  sizes,  the  lengths 
depending  upoi\  the  size  of  the  crusher  and  bin. 

Bins.  The  portable  bins  are  generally  made  with  three  com- 
partments. These  bins  are  made  in  sizes  varying  in  capacity 
from  13  to  50  tons.  In  some  of  the  more  modern  types  of  portable 
bins,  provision  is  made  so  that  the  bin  can  be  raised  to  a  height 
which  will  allow  teams  to  pass  beneath  the  unloading  chutes. 


174 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


VOIDS  AND  WEIGHTS  OF  CRUSHED  STONE.  When  rock  is 
crushed  it  occupies  a  larger  volume  than  it  did  in  place  due  to 
the  voids  in  the  mass.  The  amount  of  voids  is  variable,  de- 
pending upon  the  proportions  of  the  sizes  in  the  mass.  The 
manner  in  which  the  stone  is  placed  in  a  bin,  cart,  car,  or  barge, 
and  the  length  of  haul  also  affect  the  amount  of  voids.  Gillette 
gives  the  following,  showing  the  number  of  cubic  yards  of  broken 
stone  with  varying  percentages  of  voids  that  can  be  obtained 
from  one  cubic  yard  of  solid  rock : 


Voids 

30% 

35% 

40% 

45% 

50% 

55% 

Cubic   yards   of   broken 

stone    from     I     cubic 

yard  of  solid  rock.  .  .  . 

1-43 

1-54 

1.67 

1.82 

2.00 

2.22 

The  specific  gravities  of  the  various  rocks  used  for  building 
roads  are  given  in  Table  No.  4.  If  the  voids  in  the  mass  are 
known,  therefore,  the  weight  of  any  volume  can  be  computed. 

The  following  methods  have  been  used  in  determining  the 
voids  in  mineral  aggregates. 

Pouring  Method.  In  this  method  a  suitable  receptacle  is 
filled  with  the  dry  aggregate  to  be  tested,  the  aggregate  being 
firmly  compacted.  Water  is  then  poured  into  the  receptacle 
until  it  is  flush  with  the  surface  of  the  compacted  aggregate. 
The  amount  of  water  used  is  considered  the  amount  of  voids  in 
the  mass  of  the  aggregate. 

New  York  State  Method.  This  method  is  a  modification  of 
the  pouring  method  in  that  the  water  is  introduced  into  the  bot- 
tom rather  than  into  the  top  of  the  receptacle.  The  apparatus 
consists  of  a  i,ooo-cubic  centimeter  receptacle  open  at  the  top 
and  closed  at  the  bottom,  with  the  exception  of  a  small  orifice 
which  is  connected  by  means  of  a  rubber  tube  to  a  graduated 
burette.  The  aggregate  is  placed  in  the  receptacle  and  com- 
pacted. The  burette  is  then  filled  with  water.  The  water  is 
allowed  to  run  into  the  receptacle  through  the  orifice  in  the 
bottom.  When  the  water  is  flush  with  the  surface  of  the  com- 
pacted aggregate  the  flow  is  cut  off.  By  means  of  the  burette 


BROKEN  STONE   ROADS  175 

the  quantity  of  water  introduced  is  measured  and  this  amount 
is  considered  to  represent  the  voids  in  the  mass. 

U.  S.  Office  of  Public  Roads  Method.  A  i,ooo-cubic  centi- 
meter cylindrical  receptacle,  open  at  both  ends,  is  placed  on  a 
sheet  of  paper  and  filled  with  the  compacted  aggregate.  The 
cylinder  is  lifted  up,  allowing  the  aggregate  to  remain  on  the 
paper.  The  aggregate  is  then  poured  into  a  2,ooocubic  centi- 
meter graduated  flask  which  has  previously  been  filled  with  600 
cubic  centimeters  of  water.  The  displacement  of  the  water  in 
the  flask  is  noted.  The  amount  of  voids  in  the  mass  is  deter- 
mined by  subtracting  the  final  reading  of  the  meniscus  from 
the  initial  reading  plus  1,000,  or  1,000  +  600  —  the  final  reading 
equals  the  amount  of  voids. 

Schutte  Method.  In  this  method  a  can  having  the  shape 
of  a  truncated  cone  is  used.  It  is  necessary  in  using  this  method 
to  determine  the  specific  gravity  of  the  aggregate.  The  weight 
of  the  cone,  full  of  the  compacted  aggregate,  is  determined,  and 
next  the  weight  of  the  cone  full  of  water.  Knowing  the  weight 
of  the  cone,  the  net  weight  of  aggregate  and  water  can  be  found. 
The  weight  of  the  water  in  the  cone  multiplied  by  the  specific 
gravity  of  the  aggregate  gives  the  weight  of  solid  mass  of  the 
material  of  the  aggregate  having  a  volume  equal  to  that  of  the 
cone.  This  computed  weight  minus  the  weight  of  the  com- 
pacted aggregate  in  the  cone  gives  the  amount  of  voids  in 
the  mass. 

CONSTRUCTION 

HISTORICAL.  The  following  statements  which  are  quoted 
from  remarks  of  Tresaguet  and  McAdam  serve  to  describe  the 
methods  which  they  advocated. 

In  a  paper  presented  before  an  assembly  of  the  Departe- 
mente  des  Chaussees  in  1776,  Tresaguet  described  his  method 
of  building  roads  as  follows:  "In  order  to  successfully  diminish 
the  thickness  of  the  roads  and  give  them  sufficient  strength  to 
sustain  the  loads  which  they  have  to  carry,  it  is  necessary  to 
modify  the  method  of  construction.  ...  The  bottom  or  earth 
foundation  on  which  the  first  layer  rests  is  made  parallel  to  the 


176  ELEMENTS    OF   HIGHWAY   ENGINEERING 

finished  surface  of  the  road.  The  first  layer  of  stone  is  placed  on 
edge  similar  to  block  paving,  and  is  firmly  compacted.  More 
stone  is  likewise  placed  layer  by  layer  on  this  course  and  is 
broken  into  coarse  pieces,  which  so  interlay  that  no  voids  are 
left.  Finally,  a  top  layer  3  inches  thick  is  added.  The  stones 
in  this  layer  are  of  the  size  of  a  walnut  and  are  obtained  by 
breaking  the  stone  with  small  hammers  on  special  anvils.  This 
layer  is  placed  by  means  of  shovels  so  as  to  correspond  with 
the  desired  shape  of  the  road.  Particular  attention  should  be 
given  to  the  choice  of  stone  for  this  last  course  since  the  strength 
of  the  pavement  depends  on  it  and  one  cannot  be  too  careful 
as  to  the  quality  of  the  stone  selected.  This  may  necessitate 
at  times  a  different  grade  of  stone  for  the  top  course  than  that 
which  was  used  in  the  lower  courses." 

McAdam  said  in  various  reports  presented  by  him  during  the 
period  from  1811  to  1820:  "The  stone  laid  in  the  road  is  to  be 
loosened  up  and  broken  so  as  no  piece  shall  exceed  6  ounces 
in  weight.  The  road  is  then  to  be  laid  as  flat  as  possible,  a 
rise  of  3  inches  from  the  center  to  the  side  is  sufficient  for  a 
road  30  feet  wide.  The  stones,  when  loosened  in  the  road,  are 
to  be  gathered  off  by  means  of  a  strong,  heavy  rake,  ...  to  the 
side  of  the  road,  and  there  broken,  and  on  no  account  are  stones 
to  be  broken  on  the  road.  When  the  large  stones  have  been 
removed  and  none  left  in  the  road  exceeding  6  ounces,  the  road 
is  to  be  put  in  shape  and  a  rake  employed  to  smooth  the  sur- 
face, which  will  at  the  same  time  bring  to  the  surface  the  re- 
maining stone  and  will  allow  the  dirt  to  go  down.  When  the 
road  is  so  prepared,  the  stone  that  has  been  broken  by  the  side 
of  the  road  is  then  to  be  carefully  spread  on  it.  This  is  rather 
a  nice  operation,  and  the  future  quality  of  the  road  will  greatly 
depend  on  the  manner  in  which  it  is  performed.  The  stone 
must  not  be  laid  down  in  shovelfuls  but  scattered  over  the  sur- 
face, one  shovelful  following  another,  and  spreading  over  a  con- 
siderable space.  Every  road  is  to  be  made  of  broken  stone 
without  mixture  of  earth,  clay,  chalk,  or  any  other  matter  that 
will  imbibe  water,  and  be  affected  by  frost;  nothing  is  to 
be  laid  on  the  clean  stone  on  pretence  of  binding;  brpken  stone 


BROKEN  STONE   ROADS  177 

will  combine  by  its  own  angles  into  a  smooth  solid  surface  that 
cannot  be  affected  by  vicissitudes  of  weather,  or  displaced  by 
the  action  of  wheels,  which  will  pass  over  it  without  a  jolt  and 
consequently  without  injury.  The  size  of  stones  for  a  road  has 
been  described  in  contracts  in  several  different  ways,  sometimes 
as  the  size  of  a  hen's  egg,  sometimes  at  half  a  pound  weight. 
These  descriptions  are  very  vague,  the  first  being  an  indefinite 
size  and  the  latter  depending  upon  the  density  of  the  stone 
used,  and  neither  being  attended  to  in  the  execution.  The  size 
of  stone  used  on  a  road  must  be  in  due  proportion  to  the  space 
occupied  by  a  wheel  of  ordinary  dimensions  on  a  smooth  level 
surface,  this  point  of  contact  will  be  found  to  be,  longitudinally 
about  an  inch,  and  every  piece  of  stone  put  into  a  road,  which 
exceeds  an  inch  in  any  of  its  dimensions,  is  mischievous. 

"At  one  time  I  formed  the  opinion  that  the  use  of  a  large 
stone  foundation  was  only  a  useless  expense,  but  experience  has 
convinced  me  that  it  is  likewise  positively  injurious.  It  is  well 
known  to  every  skilful  and  observant  road  maker  that  if  strata 
of  stone  of  various  sizes  be  placed  as  a  road,  the  largest  stones 
will  constantly  work  up  by  the  shaking  and  pressure  of  traffic, 
and  that  the  only  mode  of  keeping  the  stones  of  a  road  from 
motion  is  to  use  materials  of  a  uniform  size  from  the  bottom. 
In  roads  made  upon  large  stones  as  a  foundation,  the  perpetual 
motion,  or  change  of  position  of  the  material,  keeps  open  many 
apertures  through  which  the  water  passes.  .  .  .  The  first  opera- 
tion in  making  a  road  should  be  the  reverse  of  digging  a  trench. 
The  road  should  not  be  sunk  below  but  rather  raised  above  the 
ordinary  level  of  the  adjacent  ground;  care  should  at  any  rate 
be  taken  that  there  is  sufficient  fall  to  take  off  the  water,  so 
that  it  should  always  be  some  inches  below  the  level  of  the 
ground  upon  which  the  road  is  intended  to  be  placed.  This 
must  be  done  either  by  making  drains  to  lower  the  ground 
water,  or,  if  that  be  not  practicable,  from  the  nature  of  the 
country,  then  the  soil  upon  which  the  road  is  proposed  to  be 
laid  must  be  raised  by  addition  so  as  to  be  some  inches  above 
the  level  of  the  water.  Having  secured  the  soil  from  under 
water,  the  road  maker  is  next  to  secure  it  from  rain  water,  by 


178  ELEMENTS   OF  HIGHWAY  ENGINEERING 

a  solid  road,  made  of  clean  dry  stone  or  flint,  so  selected,  pre- 
pared, and  laid,  as  to  be  perfectly  impervious  to  water.  The 
thickness  of  such  a  road  is  immaterial,  as  to  its  strength  for 
carrying  weight;  this  object  is  already  obtained  by  providing 
a  dry  surface.  .  .  .  Several  new  roads  have  been  constructed  on 
this  principle  within  the  last  three  years.  .  .  .  None  of  these 
roads  exceeds  6  inches  in  thickness,  and  although  that  on  the 
great  north  road  is  subjected  to  a  very  heavy  traffic,  it  has  not 
given  way,  nor  was  it  affected  by  the  late  severe  winter." 

SIZE  OF  STONE.  The  sizes  of  the  stone  used  vary  in  dif- 
ferent specifications.  Since  nearly  all  of  the  broken  stone  used 
for  highway  construction  is  screened  with  a  rotary  screen,  it 
should  be  noted  that  the  speed  at  which  the  screen  is  revolved, 
the  pitch,  the  length,  and  the  size  of  the  holes  in  the  screen  all 
influence  the  grading  of  the  stone  into  different  sizes.  The  type 
of  crusher  used  and  the  kind  of  rock  crushed  also  influence  the 
amount  of  the  different  sizes  obtained.  The  width  of  the  jaw 
opening  of  the  crusher  determines  the  maximum  size  of  stone 
which  will  be  obtained  from  crushing  any  rock.  The  stone 
will  be  broken  into  sizes  varying  from  this  maximum  down 
to  dust. 

Common  commercial  sizes  of  broken  stone  are  screenings, 
2/6 -inch  chips,  y2,  ^,  i,  i^,  i>£,  2,  2>^,  2>£,  and  3-inch  broken 
stone.  In  designating  the  sizes  of  broken  stone,  the  longest 
dimensions  of  the  product  have  been  stated  or  the  stone  has 
been  described,  for  instance,  as  ij^-inch  stone,  etc.  A  better 
method  of  describing  the  size  of  stone  is  to  stipulate  that  it 
shall  pass  over  a  screen  having  holes  of  one  size  and  pass  through 
a  screen  having  another  size  of  holes,  or  that  it  shall  pass  a 
screen  having  holes  of  one  size  and  be  retained  on  a  screen 
having  another  size  of  holes.  At  the  various  quarries  in  New 
York  State,  sizes  of  crusher-run  stone  in  1914  were  designated 
as  follows: 

SCREENINGS.  That  product  of  the  ordinary  run  of  the  crusher  passing  a 
5^-inch  or  jMs-inch  circular  opening  including  the  dust  of 
fracture. 

STONE.   Screenings  which  are  screened  to  remove  practically  all 
stone  dust  passing  over  a  ^-inch  or  ^-inch  screen. 


BROKEN  STONE   ROADS  179 

STONE.    Crusher  run  retained  on  the   j/£-inch  or  f^-inch  opening 
and  passing  a  i^-inch  or  iX-mcn  opening. 

STONE.    Crusher  run  retained  on  the  i^-inch  or  ij^-inch  opening 

and  passing  the  2^-inch  opening. 
2>£-iNCH  STONE.   Crusher  run  retained  on  the  2^-inch  opening  and  passing 
the  3^4-inch  opening. 

Sizes  Used  in  Different  Courses.  Broken  stone  roads  are 
ordinarily  built  in  two  or  three  courses.  The  larger  size  products 
of  the  crusher  are  used  in  the  first  or  foundation  course.  Gravel 
and  slag  are  sometimes  substituted  for  broken  stone  in  the 
foundation  course.  The  size  of  stone  for  this  course  varies 
from  i  to  3  inches  in  longest  dimensions.  The  second  course  is 
composed  of  stone  slightly  smaller,  ranging  from  i  to  2  inches 
or  from  X  mch  to  i>^  inches  in  their  longest  dimensions.  The 
top  course  consists  of  screenings  varying  from  X  mcn  down 
to  dust. 

The  sizes  of  stone,  as  specified  in  some  of  the  different  States 
of  the  United  States,  are  as  follows: 

STATE  FOUNDATION  COURSE  UPPER  COURSE 

Massachusetts                           i#  to  2}4  inches.  ^  to  \%  inches. 

New  Jersey  2^-inch  stone  or  i^-inch  stone  or 

stone  that  will  pass  a  stone  that  will  pass  a 

3-inch  ring,  minimum  2-inch  ring,  maximum 

length,  2  inches.  length,  2  inches,  mini- 
mum length,  i  inch. 

New  York  Through  zlA  -  inch  Through  2j4  -  inch 

holes.  holes. 

Maryland  3-  to  i-inch,  maxi-  i-  to  2-inch,  maxi- 
mum length,  3  inches.  mum  length,  2  inches. 


Aitken  states  that  the  broken  stone  roads  in  Great  Britain 
have  a  foundation  layer  of  stones  varying  in  size  from  3-  to  4- 
inch  cubes,  while  the  upper  course  is  composed  of  broken  stone 
varying  in  size  from  2  to  2^4  inches.  In  France  the  size  of  the 
stones  used  varies  from  about  i^  to  3  inches,  the  size  frequently 
selected  being  about  2^  inches. 

FOUNDATION  AND  SUBGRADE.  The  lower  or  foundation  course 
of  a  broken  stone  road  may  be  strengthened  by  a  telford  base,  a 
V-drain,  a  subbottom  course,  see  Fig.  69,  or  by  increasing 
its  thickness.  The  construction  of  telford  and  V-drain  foun- 
dations has  been  described  in  Chapter  V.  It  is  assumed,  of 


180 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


course,  that  the  roadbed  has  been  properly  drained  according  to 
methods  set  forth  in  Chapter  V.  The  subgrade  is  usually  a 
shallow  trench  composed  of  two  or  more  planes  or  a  curved 
surface  sloping  from  the  center  to  the  sides.  The  surface 
of  the  subgrade  is  generally  parallel  to  the  finished  surface 


FIG.  69.     Subbottom  Course. 

of  the  broken  stone  road,  although  this  is  not  true  when  the 
depth  of  stone  at  the  edge  of  the  shoulder  is  made  less  than 
at  the  center.  The  subgrade  has  the  same  width  as  the  broken 
stone  surface.  The  sides  of  the  trench,  which  serve  to  hold 
the  stone  in  place,  are  formed  by  earth  shoulders,  generally 
from  3  to  5  feet  in  width.  In  places  where  the  edge  of  the  stone 
is  bounded  by  a  curb  or  gutter,  the  earth  shoulder  is  generally 
omitted  unless  the  roadway  is  extremely  wide  and  only  a  part 
of  the  width  is  built  of  broken  stone.  The  subgrade  should  be 
brought  to  true  line  and  grade  and  be  thoroughly  compacted 
with  a  steam-roller.  Any  low  spots  which  appear  during  com- 
paction should  be  brought  up  to  grade  with  good  material  and 
rerolled. 

Form  of  Section.  Formulas  for  crown  or  transverse  slope 
suitable  for  broken  stone  roads  are  given  in  Chapter  IV.  The 
crown  ordinarily  used  is  from  %  to  J^  of  an  inch  to  the  foot.  Typ- 


BROKEN  STONE   ROADS  181 

ical  cross-sections  of  broken  stone  roads,  as  constructed  by  differ- 
ent State  Highway  Departments,  are  shown  in  Chapter  IV. 

HAULING  THE  STONE.  Stone  may  be  hauled  to  the  road 
by  means  of  any  of  the  various  carts  or  wagons  described  in 
Chapter  V.  Patent  bottom  dump-wagons  with  doors  hinged 
on  the  sides  or  on  the  ends  of  the  wagons  are  commonly  used 
and  serve  the  purpose  in  an  excellent  manner.  It  is  possible 
with  this  type  of  wagon  to  regulate  the  size  of  opening  between 
the  bottom  doors  so  that  any  width  of  opening  up  to  the  maxi- 
mum can  be  obtained.  By  this  means  it  is  possible  to  spread 
the  stone  in  layers  as  the  wagon  is  drawn  along  the  road.  Similar 
wagons  are  built  to  be  used  with  a  traction  engine.  Wagons  of 
this  type  generally  have  a  capacity  of  3  to  4  cubic  yards  and 
are  drawn  in  trains. 

LAYING  THE  STONE.  It  is  apparent  that  in  foreign  prac- 
tice somewhat  larger  stones  are  employed  for  the  upper  course 
than  are  commonly  used  in  this  country.  In  some  cases  where 
the  stone  is  not  of  a  particularly  good  quality,  better  results 
may  be  obtained  by  placing  the  smaller  stone  in  the  bottom  of 
the  road  and  the  larger  sized  stone  on  top.  There  are  also  cases 
where  the  run  of  the  crusher  from  the  coarse  sizes  down  to 
dust  is  placed  on  the  road  as  one  course,  but  this  method  is 
not  recommended.  If  the  stone  is  brought  in  patent  bottom 
dump-wagons,  it  may  be  dumped  directly  upon  the  subgrade 
and  spread  with  forks.  Stone  brought  to  the  work  for  the  upper 
courses  of  a  road,  however,  should  be  dumped  on  boards  and 
shovelled  in  place  to  prevent  the  segregation  of  the  sizes,  which 
might  occur  if  the  stone  was  dumped  directly  upon  the  road 
from  the  wagons. 

Thickness  of  Courses.  The  thickness  varies  in  different  speci- 
fications and  is  governed  by  the  amount  of  traffic  which  the 
road  is  to  receive,  the  kind  of  broken  stone,  and  the  condition 
of  the  subgrade.  For  the  foundation  course  common  values  are 
4,  6,  and  8  inches  in  total  thickness  after  rolling  where  the  sub- 
grade  furnishes  a  good  natural  foundation.  The  upper  course 
is  generally  from  2  to  3  inches  in  thickness  after  rolling.  The 
stone  surfacing  should  be  made  the  same  thickness  through- 


182  ELEMENTS   OF   HIGHWAY   ENGINEERING 

out  its  width.  Some  engineers  believe  in  economizing  by 
making  the  thickness  of  the  stone  at  the  sides  from  i  to  2 
inches  less  than  the  depth  at  the  center;  the  theory  being  that 
the  sides  do  not  receive  as  much  traffic  as  the  center.  Under 
present  traffic  conditions,  and  especially  where  heavy  motor 
trucks  are  used,  the  advisability  of  reducing  the  thickness  of 
material  at  the  sides  is  questionable. 

In  England,  Aitken  states  that  the  foundation  layer  of  3-  to 
4-inch  stones  is  made  from  6  to  9  inches  deep  in  country  dis- 
tricts and  is  increased  to  1 2  inches  for  suburban  and  town  roads. 
A  cushion  layer  of  sand  from  i  to  i^  inches  thick  is  spread 
over  the  foundation  to  prevent  the  stone  in  the  upper  course 
from  being  crushed  upon  the  hard  foundation.  The  upper  course 
of  broken  stone  is  made  from  .4  to  6  inches  thick  and  is 
constructed  in  two  layers  when  a  thickness  of  6  inches  is 
used. 

Regulating  the  Thickness.  To  gauge  the  thickness  of  a  layer 
of  stone,  wooden  cubes  made  equal  to  the  depth  of  a  layer  are 
sometimes  placed  at  intervals  across  the  roadway,  the  cubes 
being  taken  up  and  moved  along  as  the  work  progresses.  With 
this  method,  however,  if  there  are  any  irregularities  in  the 
subgrade  or  in  the  foundation  course,  they  will  be  carried  up 
to  the  finished  surface.  A  better  method  of  regulating  the 
depths  of  the  different  layers  is  to  set  strings  longitudinally  at 
the  proper  elevation  at  the  sides  and  center  of  the  roadway. 
In  this  manner  the  elevations  are  always  tied  in  with  the  finished 
grade  and  any  irregularities  can  more  readily  be  corrected  as 
they  occur. 

Rolling  the  Stone.  The  courses  are  each  laid  to  the  required 
thickness  and  separately  rolled  before  the  next  course  is  placed. 
The  roller  used  in  compacting  this  material  should  be  at  least 
ten  tons  in  weight.  Rolling  should  commence  at  one  edge  of 
the  roadway  and  progress  toward  the  center,  the  roller  travelling 
in  a  direction  parallel  with  the  center  line  of  the  road.  After 
reaching  the  middle  of  the  road,  the  roller  should  pass  to  the 
other  side,  and  again  work  in  a  similar  manner  toward  the  center. 
This  method  of  rolling  keeps  the  road  in  shape  and  -prevents 


BROKEN  STONE   ROADS  183 

either  pushing  the  crown  out  of  line  or  flattening  it.  Careful 
rolling  is  absolutely  necessary  in  order  to  obtain  a  good-  shape 
to  the  road  surface.  A  steam-roller  is  much  more  effective  than 
a  horse-roller  since  the  latter  is  lighter  and  hence  cannot  com- 
pact the  surface  so  thoroughly.  Moreover,  the  horses'  hoofs 
tend  to  loosen  the  surface  during  compaction,  which  makes  it 
difficult  to  secure  good  results.  If,  in  the  first  passages  of  the 
roller  over  the  surface,  any  low  spots  are  detected,  they  should 
immediately  be  brought  to  the  proper  level  by  the  addition  of 
more  stone  of  the  same  size  as  is  used  in  the  course  being  rolled, 
before  further  compaction  takes  place.  It  will  be  found  in  rolling 
that  broken  stone  will  be  compressed  about  33  percent;  that 
is,  to  make  a  compacted  layer  2  inches  thick,  3  inches  of  broken 
stone  would  have  to  be  spread  loose. 

In  some  specifications  it  is  stated  that  the  voids  in  the 
foundation  course  shall  be  filled  with  stone  screenings,  sand,  or 
gravel,  the  fine  binding  material  to  be  thoroughly  swept  in, 
watered,  and  rolled.  No  surplus  material,  however,  is  allowed 
to  remain  on  the  surface  of  the  foundation  course.  This  method 
of  construction  provides  a  firmer  foundation  than  where  the 
voids  between  the  stones  are  not  so  filled.  The  same  treatment 
is  also  frequently  used  to  facilitate  the  rolling  of  the  founda- 
tion course  where  the  stone  is  of  such  a  character  that  it  will 
not  readily  compact  under  the  action  of  the  roller. 

Applying  the  Screenings.  Screenings  are  generally  used  in 
connection  with  the  construction  of  the  upper  course.  When 
this  course  has  been  firmly  compacted,  the  surface  is  covered 
with  a  layer  of  stone  screenings  and  thoroughly  sprinkled  with 
water,  which  washes  the  screenings  into  the  voids  in  the  stone. 
More  screenings  are  added  as  desired  and  rolling  is  continued, 
the  surface  being  sprinkled  in  front  of  the  roller.  When  the 
proper  amount  of  water  and  screenings  has  been  used,  a  wave 
of  grout  will  be  pushed  along  in  front  of  the  roller.  A  coating 
of  screenings  should  be  laid  over  the  entire  surface,  no  more 
being  used  than  is  necessary  to  cover  the  stone.  The  stone 
screenings  resulting  from  the  crushing  of  the  rock  with  which 
the  first  two  courses  are  filled  are  generally  used  for  the  binder. 


184 


ELEMENTS   OF  HIGHWAY   ENGINEERING 


When  this  material  is  unsuitable,  clay,  loam,  sand,  or  screenings 
of  a  different  rock  are  substituted  for  it. 

COST.  The  cost  per  square  yard  of  broken  stone  roads  varies 
from  45  cents  to  $1.00.  In  the  following  table  are  given,  for  sev- 
eral localities  throughout  the  United  States,  the  average  1914 
prices  of  broken  stone  roads. 

From  Municipal  Engineering,  June,  1915. 


City 

Square 
Yards 

Price 
per 
Square  Yard 

Total 
Thickness, 
Inches 

Springfield,  Mass  

6,S2^ 

$O.S7 

6 

Providence   R   I 

f    f 

60  600 

o  6^ 

6 

New  Britain   Conn 

•12  SOO 

o  68 

7 

Auburn   N   Y 

•26  OOO 

o  70 

c 

Plainfield    N   J 

J7.QOO 

O    S7 

6 

Lansdowne   Pa 

IS  OOO 

o  80 

6 

Greenville  O                            

s.oSs 

o  60 

8 

Milwaukee   Wis                   

^,022 

I  .OS 

8K 

Kent   Wash                  

8.S71 

o.8s 

6 

Charlotte   N.  C               

17,000 

o.  so 

6 

Dade  City,  Fla  
Longview,  Tex    

140,000 
7,790 

1.40 

O.Q4 

4 
9 

MISCELLANEOUS  ROADS.  Slag  roads  and  shell  roads  have 
been  used  to  a  limited  extent  throughout  the  United  States. 
As  the  details  of  construction  are  similar  to  those  employed  in 
the  construction  of  broken  stone  roads,  certain  features,  peculiar 
to  each,  are  described  in  this  chapter. 

Slag  Roads.  Blast  furnace  slags  are  produced  in  the  manu- 
facture of  iron  and  steel  and,  in  some  cases,  are  very  similar 
in  appearance  to  close-grained  igneous  rocks.  In  reducing  iron 
ores,  the  impurities  rise  to  the  surface,  as  the  iron  melts  in  the 
furnace,  and  unite  with  the  fluxing  material.  This  material  is 
drawn  off  in  a  molten  condition  and  is  cooled  either  in  water  or 
in  the  air.  Sometimes  it  is  turned  out  onto  the  ground  in  a 
semi-molten  condition  and  forms  large  banks  of  slag.  Blast 
furnace  slag  may  be  excavated  from  slag  banks  by  means 
of  a  steam-shovel,  which  serves  to  sufficiently  break  up  the 
material  so  that  it  may  be  screened.  In  converting  the  iron 
from  the  blast  furnaces  into  steel  by  the  open-hearth  process, 


BROKEN   STONE   ROADS  185 

more  flux  is  used  in  the  process,  which  rises  to  the  surface  of 
the  molten  mass  as  slag.  The  slag  from  the  open-hearth  process 
is  generally  run  into  molds.  It  has,  in  some  cases,  been  broken 
up  in  a  rock  crusher  into  sizes  suitable  for  road  work. 

Slag  is  used  for  foundation  courses  and  in  some  instances  to 
form  the  entire  road  crust.  The  methods  used  are  similar  to 
those  described  for  the  construction  of  broken  stone  roads.  Slag 
composes  the  mineral  aggregate  of  the  Tarmac  pavements,  which 
are  built  extensively  in  the  County  of  Notts  and  elsewhere  in 
England.  This  pavement  is  described  in  Chapter  XII. 

Shell  Roads.  The  State  of  Maryland  has  built  many  miles 
of  oyster  shell  roads  along  the  eastern  shore  of  Chesapeake  Bay. 
The  shells  are  about  the  only  available  material  for  surfacing 
roads  in  that  locality.  Where  the  shells  are  simply  thrown  onto 
the  old  roadbed  without  previously  shaping  the  latter,  the  re- 
sults obtained  are  not  very  satisfactory.  The  shells  soon  push 
down  and  the  mud  works  up,  producing  conditions  which  are 
not  much  better  than  before  the  road  was  improved.  If  the 
traffic  follows  in  the  same  track  on  a  shell  road,  ruts  will  be 
quickly  formed  and  a  horse  path  will  be  made  in  the  center. 
If  these  low  places  are  immediately  filled  with  new  shells,  it 
will  tend  to  make  the  traffic  distribute  itself  over  the  surface 
and  prevent,  to  a  great  extent,  subsequent  tracking.  Shell  roads, 
unless  watered  or  treated  with  some  form  of  dust  palliative  or 
bituminous  surface,  are  liable  to  be  very  dusty. 

Good  results  with  this  material  can  be  obtained  by  following 
the  methods  used  by  the  Maryland  State  Roads  Commission. 
The  specifications  stipulate  that  the  subgrade  shall  be  firm  and 
well  rolled.  The  depth  of  the  first  course  of  shells  is  either  5 
inches  or  5  inches  at  the  center  and  3  inches  at  the  sides.  The 
depth  of  the  second  course  is  either  3  inches  or  5  inches  at  the 
center  and  3  at  the  sides.  They  are  spread  upon  the  roadbed 
with  shovels  from  piles  along  the  road  or  from  a  dumping  board. 
They  are  rolled  with  an  8-ton  roller  and  are  sprinkled  with 
water  or  bound  with  sand  during  the  process  of  rolling  until 
the  surface  is  firmly  compacted.  The  third  course  is  composed 
of  clean,  sharp  sand,  spread  just  thick  enough  to  cover  the 


186 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


second  course  after  the  latter  has  been  thoroughly  compacted. 
Shell  roads  cost  from  40  to  50  cents  per  square  yard. 


MAINTENANCE 

CAUSES  OF  WEAR.  Water,  if  allowed  to  stand  on  a  broken 
stone  surface,  will  soften  the  latter  and  cause  it  to  rapidly  wear 
out.  When  the  frost  is  coming  out  of  the  ground  in  the  spring, 


FIG.  70.     Mosaic  Condition  of  the  Surface  of  a  Broken  Stone  Road  After 
Binder  Has  Been  Swept  Away  by  Traffic. 

the  surface  will  also  be  in  a  soft  condition  and  require  atten- 
tion. The  effect  of  horse-drawn  vehicle  traffic  is  frequently 
observed  in  the  formation  of  the  "horse  path,"  so-called,  in  the 
center  of  the  road.  If  the  surface  is  given  a  flat  crown,  this 
will  be  prevented  to  some  extent  since  the  traffic  will  be  en- 
couraged to  use  the  entire  width  of  surface.  If  the  teams  track 
each  other  the  wheels  will  form  ruts,  particularly  when  the  road 
is  in  a  soft  condition.  The  grinding  action  of  the  wheels  wears 
the  stone  and  forms  dust  which,  in  a  dry  state,  is  swept  away 


BROKEN  STONE   ROADS 


187 


by  the  wind,  thus  leaving  the  stones  in  the  top  course  exposed, 
in  which  condition  they  are  liable  to  be  displaced  by  the  action 
of  traffic.  A  heavy  traffic  of  motor-cars  travelling  at  high  speed 
will  also  cause  the  broken  stone  surface  to  ravel  very  quickly 
when  the  mosaic  of  the  upper  course  is  exposed.  Sometimes 
when  the  road  is  in  this  condition  and  the  weather  has  been 
dry,  a  concentrated  motor  traffic  of  only  one  or  two  days'  dura- 


FIG.  71.    Effect  of  Motor-Car  Traffic  on  the  Surface  of  a  Broken  Stone  Road. 

tion  will  cause  ravelling.  Fig.  70  shows  the  mosaic  condition 
of  the  surface  when  the  binder  has  been  swept  away,  and  Fig. 
71  illustrates  how  a  concentrated  motor  traffic  of  short  dura- 
tion will  ravel  the  surface.  Fig.  72  shows  how  the  surface  is 
worn  out  on  the  inside  edge  of  a  curve,  as  a  result  of  motor-car 
traffic.  A  road  which  is  not  kept  in  repair  very  quickly  be- 
comes a  bad  road.  With  proper  attention,  however,  the  sur- 
face can  be  kept  in  a  passable  condition  and  the  life  of  the  road 
be  considerably  prolonged. 

ORDINARY  REPAIRS.     To  provide  against  failure  from   any 
of  the  causes  enumerated  above,  the  following  essential  princi- 


188 


ELEMENTS   OF  HIGHWAY   ENGINEERING 


pies  of  maintenance  work  are  given.  At  all  times  the  surface 
of  the  road  should  be  kept  smooth.  This  enables  the  road  to 
shed  water  more  readily  and  eliminates  shocks  which  would  re- 
sult from  the  traffic  where  the  surface  is  uneven.  Any  hollows 
or  pot-holes,  see  Fig.  73,  which  develop  in  the  surface  should 
be  reoaired  as  soon  as  formed.  Particular  attention  should  be 


FIG.  72.     Wear  on  the  Inside  of  the  Curve  Produced  by  Motor-Car  Traffic. 

given  to  eliminating  the  ruts,  since  any  depressions  in  the  sur- 
face hold  water,  and  are  enlarged  very  rapidly  by  the  ac- 
tion of  traffic.  Broken  stone  of  the  same  size  as  is  used  in 
the  upper  course  should  be  used  in  filling  in  the  depressions 
and  ruts.  In  France  and  England,  it  has  been  found  that, 
in  repairing  pot-holes,  the  best  results  are  obtained  if  the 
holes  are  cut  out  on  the  lines  of  a  square  or  rectangle 
which  is  of  sufficient  area  to  include  the  depression,  the  sides 
to  be  cut  through  for  the  full  depth  of  the  wearing  course.  The 
stone  is  replaced,  carefully  tamped,  filled  with  screenings,  and 
puddled,  or  it  is  incorporated  with  some  bituminous  material 
either  before  or  after  placing.  Rolling  in  the  spring  of  the  year 


BROKEN  STONE   ROADS 


189 


when  the  road  is  soft  will  be  of  great  help  in  providing  a  smooth 
surface  for  the  remainder  of  the  season.  An  excess  of  dust  or 
mud  on  the  surface  should  be  removed,  since  dust  is  not  only 
very  objectionable  from  the  standpoint  of  comfort  to  the  traffic, 
but  when  wet  it  forms  mud,  which  keeps  the  surface  of  the  road 
in  a  moist  condition,  sometimes  for  a  long  period.  On  the  other 


FIG.  73.     Pot-hole  in  the  Surface  of  a  Broken  Stone  Road. 


hand,  when  the  upper  course  of  stone  presents  a  mosaic  surface, 
sand,  stone  screenings,  or  other  binding  material  should  be  spread 
on  the  surface  to  prevent  ravelling. 

The  earth  shoulder  between  the  stone  surfacing  and  the 
ditch  should  be  trimmed  up  from  time  to  time,  so  that  water 
flowing  from  the  surface  of  the  road  will  not  be  impeded  in  its 
progress  to  the  ditch.  This  work  can,  in  many  cases,  be  done 
in  a  satisfactory  and  economic  manner  by  the  use  of  a  road 
scraper.  The  material  removed  from  the  shoulders,  however, 
should  never  be  thrown  up  into  the  center  of  the  stone  surface. 
As  is  the  case  in  earth  and  gravel  roads,  the  ditches  and  drains 


190  ELEMENTS   OF   HIGHWAY  ENGINEERING 

should  be  carefully  looked  after  to  provide  for  the  ready  flow 
of  water. 

The  majority  of  these  ordinary  repairs  should  be  accom- 
plished under  what  is  called  the  continuous  system  of  main- 
tenance— that  is,  a  system  where  the  roads  are  constantly  looked 
after  and  any  necessary  repairs  are  immediately  made.  Not 
only  is  the  continuous  system  of  maintenance  the  cheapest  in 
the  end,  but  it  also  keeps  the  road  in  a  good  state  of  repair. 
The  patrol  system  of  maintenance  as  carried  out  in  France  is 
a  good  illustration  of  what  can  be  accomplished  by  this  method. 
This  system  is  gradually  being  adopted  in  different  parts  of  the 
United  States,  New  York  being  the  first  State  to  adopt  this 
system  on  extensive  lines.  There  are  many  municipalities 
which  have  very  efficient  Public  Works  Departments  by  means 
of  which  the  streets  are  maintained  in  an  excellent  manner. 

RESURFACING.  When  the  road  becomes  so  badly  worn  that 
it  is  impossible  to  economically  keep  it  in  good  condition  by 
the  ordinary  methods  of  maintenance,  resurfacing  is  necessary. 
Unless  an  average  depth  of  stone  of  about  three  inches  is  to 
be  added,  the  old  broken  stone  surface  should  be  picked  up  or 
scarified  so  that  the  new  stone  will  bond  with  the  old.  The 
wheels  of  a  steam-roller  are  so  made  that  it  is  possible  to  insert 
heavy  picks  or  spikes  in  the  rear  wheels.  In  repairing  the  state 
roads  in  Massachusetts,  a  common  method  is  to  place  picks 
in  the  wheels  of  the  roller  and  to  drag  a  heavy  spike-harrow 
behind  the  roller.  A  few  trips  of  these  machines  will  loosen 
up  the  surface,  which  is  then  worked  over  with  a  light  hand 
harrow  or  a  farmer's  spring-tooth  weeder  to  bring  the  stone 
to  the  surface  and  to  shake  the  dirt  down  beneath.  The 
new  stone  is  added  wherever  required  to  bring  the  surface  to 
the  proper  shape,  and  the  surface  is  then  thoroughly  rolled  and 
puddled,  as  in  constructing  a  new  road.  The  roller  picks  will 
loosen  the  road  to  a  depth  of  from  4  to  6  inches. 

Scarifiers  are  commonly  used  in  resurfacing  work.  With 
some  types  of  scarifiers  the  picks  may  be  set  so  that  practically 
any  depth  from  i  to  6  inches  can  be  loosened.  The  scarifier 
tends  to  bring  the  stone  to  the  surface  and  to  shake  the  dirt 


BROKEN  STONE   ROADS  191 

down  underneath.  It  will  be  necessary,  however,  to  shape  up 
the  surface  with  a  harrow  or  with  rakes.  The  work  of  scarify- 
ing or  picking  will  be  much  more  readily  accomplished  if  the 
surface  is  first  soaked  with  water. 

CHARACTERISTICS 

A  broken  stone  road,  if  properly  built  of  the  right  kind  of 
stone,  is  a  very  economical  and  satisfactory  surface  for  medium 
horse-drawn  vehicle  traffic.  It  affords  an  excellent  foothold,  is 
noiseless,  does  not  offer  much  resistance  to  traffic,  and  is  com- 
fortable to  use.  In  dry  weather,  however,  a  broken  stone  sur- 
face is  usually  dusty  unless  the  surface  is  treated  with  a  palliative 
or  coated  with  bituminous  material. 


CHAPTER  IX 
BITUMINOUS  MATERIALS 

Before  considering  the  details  of  the  treatment  of  surfaces 
rendered  dustless  by  the  application  of  palliatives  and  the  con- 
struction and  maintenance  of  bituminous  surfaces,  bituminous 
pavements,  and  block  pavements  in  connection  with  which  bitu- 
minous fillers  are  employed,  the  sources,  characteristics,  and  the 
physical  and  chemical  properties  of  bituminous  materials  should 
be  considered.  The  nomenclature  of  bituminous  materials  is 
introduced  at  this  point  in  order  that  the  general  relationship 
of  materials,  their  properties  and  uses,  may  be  understood  and 
in  order  that  the  definitions  may  be  readily  accessible  for  con- 
sultation during  the  perusal  of  this  chapter.  Only  such  definitions 
have  been  introduced  as  seem  necessary  to  a  clear  understanding 
of  the  subject  matter  which  follows  in  this  and  succeeding 
chapters.  Where  definitions  have  been  used  which  include  terms 
generally  found  only  in  technical  treatises  on  the  chemistry  of 
hydrocarbons,  these  terms  have  been  printed  in  italics  and  may 
be  omitted  in  the  reading  of  the  definitions  without  depriving 
them  of  their  value  from  an  engineering  standpoint. 

NOMENCLATURE 

Definitions  which  have  been  proposed  by  the  Special  Com- 
mittee on  "Materials  for  Road  Construction"  @f  the  American 
Society  of  Civil  Engineers  are  followed  by  a  J  and  those  which 
have  been  adopted  by  the  American  Society  for  Testing  Mate- 
rials or  by  Committee  D-4  on  "Standard  Tests  for  Road  Mate- 
rials" of  this  Society  are  followed  by  a  f. 

GENERAL  DEFINITIONS. 

Bitumens  are  mixtures  of  native  or  pyrogenous  hydrocarbons 
and  their  non-metallic  derivatives,  which  may  be  gases,  liquids, 

192 


BITUMINOUS   MATERIALS  193 

viscous  liquids,  or  solids,  and  which  are  soluble  ,in  carbon 
disulphide.  ft 

Bituminous  Material.  Material  containing  bitumen  as  an 
essential  constituent.  { 

Liquid  Bituminous  Material.  Bituminous  material  showing 
a  penetration  at  normal  temperature  under  a  load  of  50  grams 
applied  for  i  second  of  more  than  35o.|{ 

Semi-Solid  Bituminous  Material.  Bituminous  material  show- 
ing a  penetration  at  normal  temperature  under  a  load  of  100 
grams  applied  for  5  seconds  of  more  than  10,  and  under  a  load 
of  50  grams  applied  for  i  second  of  not  more  than  35o.f 

Solid  Bituminous  Material.  Bituminous  material  showing  a 
penetration  at  normal  temperature  under  a  load  of  100  grams 
applied  for  5  seconds  of  not  more  than  10.  ft 

Dust  Layer.  Material  applied  to  a  roadway  for  temporarily 
preventing  the  formation  or  dispersion  under  traffic  of  distribu- 
table dust.  I 

Palliative.     A  short-lived  dust  layer.  J 

Emulsion.  A  combination  of  water  and  oily  material  made 
miscible  with  water  through  the  action  of  a  saponifying  or  other 
agent.  { 

Flux.  Bitumens,  generally  liquid,  used  in  combination  with 
harder  bitumens  for  the  purpose  of  softening  the  latter.ff 

Cut-Back  Products.  Petroleum,  or  tar  residuums,  which  have 
been  fluxed,  each  with  its  own  or  similar  distillates.  { 

Normal  Temperature.  As  applied  to  laboratory  observations 
of  the  physical  characteristics  of  bituminous  materials,  is  25°  C. 

(77°F.).t 

ASPHALTS  AND  PETROLEUMS. 

Asphalts.  Solid  or  semi-solid  native  bitumens,  solid  or  semi- 
solid  bitumens  obtained  by  refining  petroleum,  or  solid  or  semi- 
solid  bitumens  which  are  combinations  of  the  bitumens  mentioned 
with  petroleums  or  derivatives  thereof,  which  melt  upon  the 
application  of  heat  and  which  consist  of  a  mixture  of  hydro- 
carbons and  their  derivatives  of  complex  structure,  largely  cyclic 
and  bridge  compounds.^ 

Native  Asphalt.    Asphalt  occurring  as  such  in  nature,  f 


194  ELEMENTS    OF   HIGHWAY   ENGINEERING 

Petroleum.  A  natural  rock  oil  composed  of  hydrocarbons. 
(The  New  International  Encyclopaedia.) 

Blown  Petroleums.  Semi-solid  or  solid  products  produced 
primarily  by  the  action  of  air  upon  liquid  native  bitumens  which 
are  heated  during  the  blowing  process,  f 

Asphalt  Cement.  A  fluxed  or  unfluxed  asphalt  specially  pre- 
pared as  to  quality  and  consistency  for  direct  use  in  the  manu- 
facture of  bituminous  pavements,  and  having  a  penetration  at 
25°  C.  (77°  F.)  of  between  5  and  250,  under  a  load  of  100  grams 
applied  for  5  seconds,  f 

Rock  Asphalt.  Sandstone  or  limestone  naturally  impregnated 
with  asphalt.  J 

TARS. 

Tars.  Bitumens  which  yield  pitches  upon  fractional  distilla- 
tion and  which  are  produced  as  distillates  by  the  destructive 
distillation  of  bitumens,  pyrobitumens  or  organic  materials.! 

Coal  Tar.  The  mixture  of  hydrocarbon  distillates,  mostly 
unsaturated  ring  compounds,  produced  in  the  destructive  distil- 
lation of  coal.fj 

Gas-House  Coal  Tar.  Coal  tar  produced  in  gas-house  re- 
torts in  the  manufacture  of  illuminating  gas  from  bituminous 
coaLtt 

Coke-Oven  Tar.  Coal  tar  produced  in  by-produce  coke  ovens 
in  the  manufacture  of  coke  from  bituminous  coal,  ft 

Water-Gas  Tars.  Tars  produced  by  cracking  oil  vapors  at 
high  temperatures  in  the  manufacture  of  carburetted  water-gas,  f 

Refined  Tar.  Tar  freed  from  water  by  evaporation  or  dis- 
tillation which  is  continued  until  the  residue  is  of  desired  con- 
sistency; or  a  product  produced  by  fluxing  tar  residuum  with 
tar  distillate,  ft 

Pitches.  Solid  residues  produced  in  the  evaporation  or  dis- 
tillation of  bitumens,  the  term  being  usually  applied  to  residues 
obtained  from  tars.Jt 

USE  OF  BITUMINOUS  MATERIALS. 

Bituminous  Surface.  A  superficial  coat  of  bituminous  mate- 
rial with  or  without  the  addition  of  stone  or  slag  chips,  gravel, 
sand,  or  material  of  similar  character.  { 


BITUMINOUS   MATERIALS  195 

Bituminous  Pavement.  One  composed  of  stone,  gravel,  sand, 
shell,  or  slag,  or  combinations  thereof,  and  bituminous  materials 
incorporated  together.  } 

Bituminous  Macadam  Pavement.  One  having  a  wearing 
course  of  macadam  with  the  interstices  filled  by  penetration 
methods  with  a  bituminous  binder.} 

Bituminous  Concrete  Pavement.  One  composed  of  stone, 
gravel,  sand,  shell,  or  slag,  or  combinations  thereof,  and 
bituminous  materials  incorporated  together  by  mixing 
methods.  } 

Asphalt  Block  Pavement.  One  having  a  wearing  course  of 
previously  prepared  blocks  of  asphaltic  concrete.} 

Sheet  Asphalt  Pavement.  One  having  a  wearing  course  com- 
posed of  asphalt  cement  and  sand  of  predetermined  grading,  with 
or  without  the  addition  of  fine  material,  incorporated  together 
by  mixing  methods.} 

Rock  Asphalt  Pavement.  A  wearing  course  composed  of 
broken  or  pulverized  rock  asphalt  with  or  without  the  addition 
of  other  bituminous  materials.} 

The  Special  Committee  of  the  American  Society  of  Civil 
Engineers  on  "Materials  for  Road  Construction,"  in  its  1913 
Report,  advisedly  called  attention  to  the  misuse  of  two  of  the 
terms  mentioned  above.  "Your  Committee,  recognizing  an  un- 
fortunate tendency  to  use  as  the  generic  expression  the  terms 
'bituminous  material'  and  'bitumen'  synonymously,  recommends 
that  the  term  'bituminous  material'  be  used  as  a  generic  ex- 
pression when  referring  to  road  and  paving  materials  containing 
bitumen  and  that  the  term  'bitumen'  be  used  in  a  restricted 
sense  as  covered  by  the  following  definition  adopted  by  the 
American  Society  for  Testing  Materials.  'Bitumens  are  mix- 
tures of  native  or  pyrogenous  hydrocarbons  and  their  non-metallic 
derivatives,  which  may  be  gases,  liquids,  viscous  liquids,  or 
solids,  and  which  are  soluble  in  carbon  disulphide.'  An  illus- 
tration of  ambiguity  in  the  use  of  the  two  terms  may  be  found 
in  some  descriptions  of  bituminous  pavements  where  a  bitumi- 
nous cement,  only  75  percent  soluble  in  carbon  disulphide,  was 
used.  In  the  general  description  of  these  pavements,  the  word 


196  ELEMENTS   OF   HIGHWAY  ENGINEERING 

'bitumen'  was  used  to  refer  to  the  material  as  a  whole,  while 
in  giving  the  analysis  of  the  mix,  the  word  'bitumen'  was  used 
to  refer  only  to  that  portion  of  the  cement  soluble  in  carbon 
disulphide."  In  its  1915  Report,  the  Committee  strongly  advised 
the  discontinuance  of  the  use  of  the  terms  "liquid  asphalt"  and 
"asphaltic  content,"  as  these  terms  are  meaningless  in  most 
cases.  Committee  D-4  of  the  American  Society  for  Testing 
Materials  has  very  properly  recommended  the  discontinuance 
of  the  use  of  the  term  "artificial  asphalt"  and  has  stated  in  its 
1915  Report  to  the  Society  that  "Liquid  Asphalt"  is  a  trade 
name  not  subject  to  definition. 

SOURCES,  MINING  AND  MANUFACTURE 

The  crude  materials  from  which  are  manufactured  the  bitu- 
minous materials  that  are  used  in  the  construction  and  main- 
tenance of  roads  and  pavements  may  be  classified  as  follows: 
Rock  Asphalts;  Asphalts;  Petroleums;  Gas-House  Coal  Tars; 
Coke-Oven  Tars;  and  Water-Gas  Tars.  Table  No.  5,*  com- 
piled by  Prevost  Hubbard,  shows  graphically  the  interrelation- 
ship between  the  principal  types  of  bituminous  materials  and 
their  derivatives.  The  three  bituminous  materials,  asphalts, 
petroleums,  and  tars,  form  the  basis  of  the  table.  After  water 
and  other  impurities  have  been  removed  from  the  crude  mate- 
rials, the  three  diagrams  show  the  by-products  which  are  obtained 
by  processes  of  refining.  The  various  portions  of  this  table 
should  be  reread  in  connection  with  the  descriptions  of  the 
refining  processes  used  for  the  manufacture  of  palliatives,  sur- 
facing materials,  bituminous  cements,  and  fillers  from  the  several 
materials. 

ROCK  ASPHALTS.  The  rock  asphalts  in  common  use  in 
Europe  are  composed  of  limestones  and  sandstones  impregnated 
with  7  to  14  percent  of  asphalt.  The  principal  sources  are  in 
France,  Switzerland,  Alsace,  Sicily,  and  Germany.  The  rock 
asphalts  of  the  United  States  are  found  principally  in  California, 
Kentucky,  Oklahoma,  and  Utah. 

*  See  Journal  of  the  Franklin  Institute,  April,  1912. 


BITUMINOUS   MATERIALS 


197 




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ELEMENTS   OF   HIGHWAY  ENGINEERING 


ASPHALTS.  Asphalts,  according  to  the  definition  previously 
quoted,  may  be  considered  as  belonging  to  one  of  the  three 
following  classes:  (i)  solid  or  semi-solid  native  bitumens;  (2) 
solid  or  semi-solid  bitumens  obtained  by  refining  petroleums; 
(3)  solid  or  semi-solid  bitumens  which  are  combinations 


Courtesy  of  Mr.  C.  N.  Forrest. 

FIG.  74.     Mining  Trinidad  Lake  Asphalt. 

of  the  bitumens  mentioned  with  petroleums,  or  derivatives 
thereof. 

The  Alcatraz,  Bermudez,  Cuban,  Gilsonite,  Maracaibo,  and 
Trinidad  asphalt  cements  contain  asphalt  as  defined  under  the 
first  group,  that  is,  "asphalts  are  solid  or  semi-solid  native 
bitumens,  etc." 

The  asphalts  obtained  by  refining  such  asphaltic  oils  as  are 
obtained  from  the  fields  of  California,  Mexico,  Southern  Illinois, 
and  Texas  come  within  the  second  group,  that  is,  "asphalts 
are  solid  or  semi-solid  bitumens  obtained  by  refining  petro- 
leums, etc." 


BITUMINOUS   MATERIALS  199 

The  asphalts  made  from  a  combination  of  refined  petro- 
leum and  Gilsonite,  a  solid  native  bitumen,  are  covered  by 
the  third  group  to  which  reference  has  been  made,  namely, 
" asphalts  are  solid  or  semi-solid  bitumens  which  are  combina- 
tions of  the  bitumens  mentioned  with  petroleum  or  deriva- 
tives thereof,  etc." 

Trinidad  and  Bermudez  Asphalts.*  "Trinidad  and  Bermudez 
Lake  asphalts  are  denominated  native  asphalts  because  they  are 
found  in  nature  in  solid  form  as  distinguished  from  others  which 
are  derived  from  liquid  bitumen  by  industrial  processes  and 
become  asphalt  by  reason  of  the  manipulation  of  such  processes. 
They  are  also  denominated  Lake  asphalts  because  they  occur 
upon  the  surface  of  the  earth  in  a  single  mass  like  so  much 
water  or  paste  in  a  large  bowl  or  lake. 

'  The  pitch  lake  of  the  Island  of  Trinidad  is  situated  about 
one  mile  from  the  sea,  on  the  highest  part  of  La  Brea  Point, 
138.5  feet  above  sea  level.  It  lies  apparently  in  the  crater  of 
an  extinct  mud  volcano  having  a  nearly  circular  area  of  114.67 
acres.  The  lake  is  filled  to  a  depth  of  more  than  135  feet  at 
the  center  with  a  uniform  mass  of  asphalt,  which  must  amount 
to  many  millions  of  tons. 

"The  Bermudez  Pitch  Lake  lies  about  thirty  miles  from  the 
northeast  coast,  in  the  State  of  Sucre,  Venezuela,  which  forms 
the  opposite  side  of  the  Gulf  of  Paria  from  the  Island  of  Trinidad. 
It  covers  an  area  of  about  1,200  acres  to  a  maximum  depth  of 
10  feet. 

"Crude  Trinidad  and  Bermudez  Lake  asphalt  is  gathered 
from  the  deposits  by  native  laborers  who  strip  off  the  over- 
lying vegetation  when  necessary  and  flake  out  the  asphalt 
in  large  chunks  with  picks  or  mattocks.  (See  Fig.  74.)  Crude 
Lake  asphalt  is  transported  in  bulk  in  the  hold  of  the  steam- 
ers which  are  engaged  in  that  particular  trade  and  carry 
single  cargoes  up  to  as  much  as  five  or  six  thousand  tons,  if 
desired.  The  asphalt  when  placed  in  vessels  flows  together 

*  See  1913-1914  Lecture  by  C.  N.  Forrest,  Chief  Chemist,  Barber  Asphalt 
Paving  Company,  on  "Trinidad  nd  Bermudez  Asphalts,"  in  the  Graduate 
Course  in  Highway  Engineering,  at  Columbia  University. 


200  ELEMENTS   OF   HIGHWAY  ENGINEERING 

and  again  becomes  a  solid  mass.    It  has  the  following  general 
characteristics: 


Crude 
Trinidad 
Lake 
Asphalt 

Crude 
Bermudez 
Lake 
Asphalt 

Weight  per  cubic  foot  

7S  Ibs 

66  Ibs 

Water    

29  o% 

Bitumen  soluble  in  CS>  

72    O% 

Other  matter 

12    0% 

i    0% 

"Crude  Lake  asphalt  is  refined  in  order  to  remove  from  it 
those  substances  which  are  useless  for  the  purposes  for  which 
the  refined  asphalt  is  employed.  These  are  chiefly  water  and  a 
small  amount  of  twigs,  branches  of  trees  or  other  vegetable 
matter  which  has  accidentally  found  its  way  into  the  lakes. 
The  crude  asphalt  is  too  solid  to  pump  through  a  pipe-line  and 
must  therefore  be  handled  in  buckets  to  the  refining  kettles. 
The  refining  kettles  are  made  of  steel  and  are  rectangular  in 
shape.  They  are  open  at  the  top  in  order  to  facilitate  charging 
with  the  asphalt  and  the  escape  of  water.  These  kettles  are 
12  feet  by  24  feet  by  9  feet  6  inches  deep  and  have  a  capacity 
of  70  tons  of  Trinidad  or  50  tons  of  Bermudez  asphalt.  They 
are  equipped  with  steam  coils  consisting  of  about  4,000  feet  of 
i^-inch  pipe,  through  which  steam  under  a  pressure  of  125 
to  150  pounds  is  circulated.  They  are  also  equipped  with  a  sys- 
tem of  perforated  pipes  laid  upon  the  bottom  of  the  kettle  from 
which  live  steam  is  blown  through  the  asphalt  in  order  to  hasten 
the  evaporation  of  water  and  to  prevent  sedimentation.  The 
crude  asphalt  is  dumped  into  such  kettles  and  heated  to  a 
temperature  of  325°  to  350°  F.,  which  reduces  it  to  a  liquid 
condition,  until  all  water  is  eliminated  and  a  standard  uniform 
consistency  has  been  reached.  From  8  to  10  hours  is  required 
for  the  dehydrating  process,  after  which  any  foreign  substances 
found  floating  upon  the  surface  of  the  asphalt  are  removed  by 
skimming.  The  refining  operation,  which  is  carried  on  at  a  rel- 
atively low  temperature  and  with  a  copious  live  steam  agitation, 
leaves  the  dehydrated  bitumen  without  alteration  and  in  as 


BITUMINOUS   MATERIALS  201 

nearly  its  natural  condition  as  it  is  possible  to  conceive.  After 

it  is  refined  the  lake  asphalt  has  the  following  general  char- 
acteristics : 


Refined 
Trinidad 
Lake 
Asphalt 

Refined 
Bermudez 
Lake 
Asphalt 

Specific  Gravity  at  77°  F  .  .           

I  .40 

I    08 

Penetration  at  77°  F.,  100  grams,  5  seconds  

2  to  4 

18  to  20 

Bitumen  soluble  in  CS2 

c6  s% 

04.   4.% 

"Refined  lake  asphalt  is  run,  while  still  in  a  molten  condition 
and  at  a  temperature  of  about  300°  F.,  into  soft  wood  barrels 
which  have  been  previously  coated  on  the  inside  with  clay  so 
that  the  asphalt  will  not  stick  to  the  wood." 

Maracaibo  and  Cuban  Asphalts.*  "In  Venezuela  is  located 
the  Maracaibo  deposit,  about  fifty  miles  inland  from  the  Gulf 
of  Maracaibo.  There  are  a  number  of  deposits  in  the  vicinity 
and  the  asphalt  appears  to  originate  in  maltha  or  tar  springs 
as  does  the  Bermudez  deposit,  the  maltha  having  become  hard- 
ened by  exposure  to  a  semi-solid,  nearly  pure,  asphalt.  The 
character  of  the  material  is  quite  different  from  the  Bermudez 
asphalt^  and  it  is  recognizable  by  its  particularly  rank  odor 
and  the  peculiar  gummy  nature  of  the  impurities  with  which 
it  is  contaminated.  The  Maracaibo  deposit  has  been  of  variable 
commercial  importance,  possibly  on  account  of  the  difficulty  of 
access,  and  its  use  has  been  limited  in  recent  years  to  compara- 
tively few  localities. 

"On  the  Island  of  Cuba  there  are  a  large  number  of  de- 
posits of  various  kinds  of  asphalts.  The  only  one  of  large  extent 
is  located  in  the  Pinar  del  Rio  province,  about  forty  miles  west 
of  Havana  and  about  five  miles  from  Mariel  Bay,  from  which 
the  deposit  takes  its  name.  This  material  has  been  used  in 
the  United  States  for  about  ten  years  and  has  attained  con- 
siderable importance.  The  asphalt  of  these  Mariel  deposits  is 
a  very  hard  material  resembling,  in  its  crude  state,  bituminous 

*  Lester  Kirschbraun,  Consulting  Chemical  Engineer,  in  May,  1912, 
Journal  of  the  Western  Society  of  Engineers. 


202  ELEMENTS   OF   HIGHWAY   ENGINEERING 

coal.  It  contains  about  56  to  60  percent  of  pure  bitumen  and 
about  40  percent  of  mineral  matter.  Like  the  Trinidad  mate- 
rial, there  is  great  uniformity  in  the  proximate  composition  of 
the  asphalt  from  different  sections  of  the  deposit.  The  asphalt 
occurs  in  immense  seams  and  veins,  some  of  which  may  be 
followed  for  several  miles  across  country  by  their  outcroppings. 
Certain  of  the  seams  lie  horizontally,  and  have  been  worked 
by  open  cuts  to  a  convenient  depth,  following  the  seams  in 
their  general  trend.  At  another  point  of  outcropping,  the  mate- 
rial has  been  obtruded  in  a  vertical  direction  and  the  excavation 
of  open  pits  has  followed  the  crude  material  downward." 

Alcatraz  Asphalt.*  aln  California  there  are  certain  deposits 
of  large  extent  which  were,  in  the  early  nineties,  of  considerable 
importance.  Alcatraz  asphalt  was  a  well-known  brand  of  such 
material.  The  development  of  the  oil-asphalt  industry  in  Cali- 
fornia made  it  commercially  impracticable  to  work  these  natural 
asphalt  deposits,  and  there  is  now  no  solid  natural  California 
asphalt  upon  the  market." 

Gilsonite  Asphalt,  f  "Gilsonite  is  a  solid  native  bitumen 
found  in  the  United  States  in  Utah  and  Colorado.  It  breaks 
with  a  concoidal  fracture  and  has  a  reddish-brown  streak.  This 
material  is  found  in  fissure  veins  varying  in  thickness  from  a 
few  inches  to  5  or  6  feet.  (See  Fig.  75.)  On  account  of  being 
very  brittle  it  is  easy  to  mine,  the  most  common  method  being 
by  the  use  of  picks.  Successful  results  have  been  obtained  by 
using  steam,  which  is  turned  into  certain  workings  of  the  mine 
long  enough  to  cause  the  Gilsonite  to  expand  and  soften.  As 
the  Gilsonite  cools,  after  the  steam  is  shut  off,  it  contracts  and 
breaks  into  chunks.  It  is  then  brought  to  the  surface  of  the 
mine  and  put  into  burlap  sacks  which,  when  full,  weigh  from 
200  to  300  pounds  each. 


*  Lester  Kirschbraun,  Consulting  Chemical  Engineer,  in  May,  1912, 
Journal  of  the  Western  Society  of  Engineers. 

f  From  1912-1913  Lecture  by  H.  B.  Pullar,  General  Manager,  The  Pioneer 
Asphalt  Company,  on  "The  Mining  of  Gilsonite  and  the  Manufacture  of 
Gilsonite  Asphalt"  in  the  Graduate  Course  in  Highway  Engineering,  at 
Columbia  University. 


BITUMINOUS   MATERIALS 


203 


'The  following  analysis  is  typical  of  Gilsonite* 


Specific  gravity 1 . 033 

Melting  point 291°  F. 

Bitumen  soluble  in  carbon  disulphide 99-58% 

"In  the  manufacture  of  Gilsonite  products  various  propor- 
tions of  Gilsonite  are  used,  depending  upon  the  quality  and 


a±. 


Courtesy  of  Mr.  H.  B.  Pullar. 

FIG.  75.     Veins  of  Gilsonite  Asphalt. 

consistency  of  the  material  desired.  Gilsonite  rapidly  combines 
with  heavy  residuum  oil,  the  best  results  being  obtained  from 
fluxing  Gilsonite  with  a  semi-asphaltic  or  asphaltic  base  oil, 
although  for  certain  purposes  paraffin  oils  prove  most  desirable. 
In  producing  asphalt  products  from  Gilsonite,  the  oil  must  be 
of  a  suitable  quality  and  must  be  carefully  prepared  without 
cracking.  The  best  method  for  determining  this  is  by  the  use 
of  a  microscope,  as  any  cracking  which  takes  place  in  the  oil 
shows  up  in  specks  of  free  carbon  under  the  microscope. 

"The  oil  is  heated  to  a  temperature  of  not  less  than  425°  F., 
at  which  temperature  the  Gilsonite  is  slowly  added  and  dis- 


204  ELEMENTS   OF   HIGHWAY  ENGINEERING 

tributed  throughout  the  mass  of  oil  as  much  as  possible.  The 
oil  should  be  in  a  state  of  agitation  as  this  is  of  considerable 
assistance  in  rapidly  melting  the  Gilsonite  which  goes  into  a 
perfect  solution  with  the  hot  oil,  making  a  homogeneous  mass 
and  changing  materially  the  characteristics  of  the  oil.  Gilsonite 
adds  life  to  the  product  and  prevents  the  oil,  to  a  very  large 
extent,  from  oxidizing  or  hardening  up. 

"In  a  great  many  instances,  and  especially  in  producing 
those  products  which  are  little  affected  by  changes  in  tempera- 
ture, the  oil  is  first  treated  with  air  before  the  Gilsonite  is  added. 
Treating  the  oil  with  air  tends  to  very  materially  change  the 
characteristics  of  the  oil,  the  batch  gradually  thickening  until 
it  becomes  a  semi-solid.  The  length  of  treatment  depends  upon 
the  consistency  of  the  material  desired  and  varies  from  10  to 
40  hours.  In  this  treatment  with  air,  the  oil  is  first  put  into 
a  semi-open  still  and  brought  to  a  temperature  of  350°  F.,  at 
which  temperature  air  is  gradually  added  to  the  batch.  The 
temperature  rises  until  it  reaches  about  425°  F.,  which  tempera- 
ture is  maintained  for  a  period  of  time,  depending  upon  the 
results  desired." 

Petroleums.*  "  The  petroleum  oils  of  this  country  are  gener- 
ally classed  into  three  groups,  known  as  paraffin,  semi-asphaltic, 
and  asphalt  petroleums.  The  oils  of  the  Pennsylvania  fields 
are  paraffin  base  oils.  Those  of  the  Illinois,  Kansas,  Oklahoma 
and  Gulf  fields  are  semi-asphaltic  to  varying  degrees.  The  Cali- 
fornia oils  are  generally  considered  asphaltic.  No  artificial 
asphalt  is  made  from  the  Pennsylvania  or  paraffin  oils,  but 
large  quantities  are  produced  from  the  oils  of  the  semi-asphaltic 
and  California  group. 

"  The  earliest  oil  asphalt  of  this  country  was  produced  as  a 
by-product  from  the  straight  distillation  of  California  crude 
petroleums.  The  early  asphalt  so  produced  fell  into  disrepute 
on  account  of  the  careless  manner  of  production,  the  lack  of 
uniformity,  and  the  inferiority  of  the  product  through  improper 
methods  of  distillation.  The  demand  for  a  better  quality  has 

*  Lester  Kirschbraun,  Consulting  Chemical  Engineer,  in  May,  1912, 
Journal  of  the  Western  Society  of  Engineers.  « 


BITUMINOUS    MATERIALS  205 

induced  improvement  in  refining  methods,  which  has  resulted 
in  recent  years  in  superior  products  being  prepared  especially 
for  paving  purposes. 

"There  are  at  present  two  methods  used  in  preparing  oil 
asphalts,  which  methods  are  more  or  less  adaptable  according 
to  the  character  of  the  oil  operated  upon.  The  first  method  is 
that  of  ordinary  distillation  of  the  crude  petroleum  with  the 
use  of  saturated  steam,  the  distillation  being  carried  on  until 
the  solid  or  asphaltic  portion  of  the  oil  remains.  The  distilla- 
tion is  carried  on  in  large  stills  holding  from  300  to  1,000  barrels 
of  oil.  Steam  is  injected  into  the  bottom  of  the  stills  through 
perforated  pipes  to  effect  agitation  and  assist  in  the  removal 
of  the  volatile  oils.  In  the  best  practice,  steam  is  also  injected 
at  the  top  of  the  stills  to  facilitate  carrying  off  the  heavy  oil 
vapors,  and  to  prevent  their  decomposition  by  condensation 
and  dropping  back  into  the  hot  oil.  The  maximum  tempera- 
ture employed  in  careful  practice  rarely  exceeds  700°  F.  The 
material  in  the  stills  is  brought  to  the  desired  consistency  and 
run  into  cooling  stills  or  through  pipes  cooled  by  oil  used  for 
succeeding  charges.  Sometimes  the  material  from  several  stills 
is  run  into  one  large  receiving  still,  where  it  is  mixed  with  other 
batches  and  a  greater  degree  of  uniformity  thereby  attained. 
Aside  from  the  kind  of  oil  used,  the  value  of  the  product  of 
this  distillation  process  depends  upon  the  various  means  of  pre- 
venting local  overheating  and  decomposition,  the  amount  and 
efficient  distribution  of  steam  injected,  the  time  of  the  distilla- 
tion, and  the  temperatures  employed.  There  are  commercial 
asphalts  prepared  in  this  way  from  California,  Mexico,  and 
Texas  oils. 

"This  brings  us  to  a  second  method  of  preparation  of  asphaltic 
products  by  air  blowing.  That  method  has  been  developed 
particularly  through  an  effort  to  utilize  petroleum  residuums  of 
the  character  not  reducible  by  the  distillation  process  described. 
Asphalts  prepared  by  this  method  are  commercially  known  as 
blown-oil  asphalts.  In  the  preparation  of  blown-oil  asphalts, 
petroleum  residuum  is  the  raw  material.  This  petroleum  re- 
siduum is  prepared  as  the  residue  from  the  distillation  of  crude 


206  ELEMENTS   OF  HIGHWAY   ENGINEERING 

petroleums  with  steam  through  the  lubricating  oil  fractions,  and 
is  continued  in  the  best  practice,  with  the  removal  of  as  much 
of  the  vaseline  (if  present)  as  can  be  accomplished  without 
decomposition.  The  air-blowing  operation  is  conducted  in  open 
kettles  equipped  with  perforated  pipes  along  the  bottom.  The 
residuum  is  kept  at  a  temperature  much  below  that  at  which 
normally  it  distills,  and  air  is  injected  into  the  mass  through 
the  perforated  pipes,  producing  a  violent  agitation  and  intimate 
contact  between  the  residuum  and  air.  The  injection  of  air 
under  these  conditions  produces,  among  other  reactions,  oxida- 
tion and  condensation  of  the  hydrocarbons  of  the  residuum. 
The  oil  treated  gradually  thickens  and  the  process  is  continued 
until  a  product  of  the  desired  consistency  is  obtained.  A  sig- 
nificant characteristic  of  the  process  is  that  there  is  no  material 
loss  during  the  operation." 

TARS.  The  refined  tars  and  pitches  used  in  the  construction 
and  maintenance  of  various  types  of  roads  and  pavements  are 
manufactured  from  gas-house  coal  tars,  coke-oven  tars,  and 
water-gas  tars. 

Gas-House  Coal  Tar.*  "In  classifying  coal  tars  for  use  in 
road  work  it  is  customary  to  group  them,  in  accordance  with 
the  method  of  manufacture,  into  gas-house  tars  and  coke-oven 
tars.  The  following  table  (abstracted)  gives  roughly  the  char- 
acteristic differences  in  the  two  tars: 


Gas  tar 
Percent 

Coke  oven  tar 
Percent 

Creosote  oil  .  .                   

8.6 

14.5 

Anthracene  oil 

17.4 

27.  ^ 

Pitch 

58.4 

44-  ^ 

Carbon                                                                                  .  . 

I5-2S 

5-8 

"As  gas  houses  are  usually  run  for  the  production  of  the 
largest  possible  yield  of  gas  from  a  ton  of  coal,  the  highest 
possible  temperatures  are  employed,  and  the  tar  produced  has, 
in  consequence,  usually  a  maximum  amount  of  free  carbon.  This, 

*  See  1912-1913  Lecture  by  Philip  P.  Sharpies,  Chief  Chemist,  Barrett 
Manufacturing  Company,  on  "The  Manufacture  of  Refined  Coal  Tar,"  in 
the  Graduate  Course  in  Highway  Engineering  at  Columbia  University. 


BITUMINOUS   MATERIALS  207 

however,  is  not  always  so  and  low  carbon  tars  ijaay  be  made 
at  gas  houses.  Very  recently  there  has  been  installed  at  a 
number  of  gas  houses  in  the  United  States  a  new  form  of  retort, 
differing  essentially  from  the  older  small  horizontal  retort.  These 
new  retorts  are  either  inclined  or  vertical,  to  permit  of  the 
handling  of  the  coke  by  gravity  and  by  mechanical  means. 
The  form  of  the  retort  leads  to  low  temperatures  in  the  coking 
of  the  coal,  and  the  escape  of  the  tar  and  gases  through  com- 
paratively cool  passages.  The  tars  resulting  from  these 
forms  of  ovens  may  show  even  lower  carbons  than  the  coke- 
oven  tars. 

"The  collection  of  the  tar  as  it  is  evolved  from  the  retort 
is  essentially  the  same  in  principle  in  the  two  types  of  gas  plants. 
The  tar,  owing  to  the  high  temperature,  goes  off  as  a  vapor 
mingled  with  the  gases.  Condensed,  however,  at  a  compara- 
tively high  temperature,  the  greater  part  is  deposited  in  the 
large  collecting  gas  main  known  as  the  hydraulic  main,  where 
it  is  trapped  and  led  to  the  storage  tank.  Some  further  part 
is  deposited  in  the  condensers,  where  the  temperature  of  the 
gas  is  brought  down  by  passing  over  water-cooled  surfaces  to  a 
workable  temperature.  Part  of  the  tar,  however,  is  so  finely 
divided  mechanically  that  it  is  carried  on  by  the  stream  of  the 
gas  through  the  condensers.  The  method  of  removing  the  last 
particles  of  tar  from  the  gas  varies  greatly  in  different  plants 
but  usually  a  system  of  baffle  plates  is  used  which  coalesces 
the  particles  of  tar  by  impinging  them  upon  the  opposed  plates. 
The  tar  collected  in  these  several  places  is  all  conducted  to  the 
same  storage  tank. 

"The  first  process  in  refining  tar  is  the  removal  of  the  water. 
The  presence  of  a  large  amount  of  water  leads  to  frothing  in 
the  still,  making  the  process  of  distillation  extremely  slow,  and 
in  case  the  still  actually  froths  over,  to  the  loss  of  the  charge. 
The  most  successful  method  in  use  at  the  present  time  is  to 
pass  the  tar  in  thin  films,  at  about  the  temperature  of  boiling 
water,  through  vacuum  chambers.  This  results  in  the  elimina- 
tion of  a  large  percentage  of  water,  and  also  to  the  driving  off 
of  some  of  the  light  oils,  which  are  condensed  and  recovered 


208  ELEMENTS   OF  HIGHWAY  ENGINEERING 

from  the  vapors.  But  it  is  usually  not  possible  even  by  this 
method  to  reduce  the  water  below  i  percent. 

"After  the  stills  are  charged  with  the  correct  blend  of  tars 
to  produce  the  desired  results,  the  fires  are  started  and  the 
mixture  heated  carefully  to  about  100°  C.  The  water,  together 
with  the  light  oils,  is  driven  off.  The  distillation  once  started 
continues  to  about  220°  C.  Then  the  flow  of  the  liquor  becomes 
less  and  the  temperature  is  increased  until  the  oil  begins  to 
come  off  freely  once  more. 

"In  the  manufacture  of  the  very  lightest  refined  road  tars 
the  distillation  is  carried  only  to  the  point  where  the  water  is 
completely  driven  off.  In  England  and  on  the  Continent  this 
constitutes  the  major  portion  of  the  refined  tar  used  for  road 
purposes,  applicable  to  surface  treatment  of  a  road,  especially 
where  a  very  thin  coat  is  desired.  In  case  the  material  to  be 
manufactured  is  to  be  used  for  road  construction,  the  firing  on 
the  still  is  continued  much  longer,  and  much  more  of  the. oil 
taken  off.  It  is  customary  in  this  case,  in  order  that  the  vis- 
cosity of  the  material  may  be  closely  regulated,  to  subdue  the 
fire  before  the  end  point  is  reached.  Then,  in  order  to  raise 
the  viscosity  to  the  required  point,  air  or  steam  is  blown  through 
the  hot  tar  in  the  still,  to  remove  further  oils  and  bring  the  tar 
to  the  desired  consistency.  This  'blowing/  as  it  is  called,  be- 
comes much  more  important  as  the  melting  point  of  the  pitch 
is  increased.  With  pitches  used  in  paving  work  the  blowing  of 
the  tar  is  commenced  much  earlier  than  the  finishing  point,  in 
order  to  agitate  the  contents  of  the  still  and  prevent  the  depo- 
sition of  carbon  on  the  bottom.  If  this  carbon  is  allowed  to 
deposit,  local  heating  of  the  plates  takes  place  and  the  still  is 
quickly  ruined. 

"After  the  tests  in  the  laboratory  have  shown  the  refined 
tar  to  be  of  the  correct  consistency,  the  material  is  either  run 
off  by  gravity  to  cooling  tanks,  or  in  case  the  stills  are  on  a  low 
level,  it  is  forced  over  by  compressed  air  or  by  steam  pressure, 
into  the  coolers.  The  coolers  are  simply  iron  tanks  open  on  all 
sides,  so  as  to  allow  the  free  circulation  of  air  and  a  quick  cooling 
of  the  pitch.  The  cooling,  however,  even  under  favorable  cir- 


BITUMINOUS   MATERIALS  209 

cumstances,  requires  a  long  time,  and  in  the  case  of  Jarge  cooling 
tanks  several  days  elapse  before  the  tar  is  of  a  temperature 
safe  to  run  into  barrels." 

Coke-Oven  Tar.*  "There  are  two  general  types  of  coke 
ovens  in  use  at  present,  in  one  of  which  no  attempt  is  made 
to  recover  the  volatile  products  of  the  coal.  This  is  the  oldest 
form  of  oven,  known  as  the  'beehive,'  and  is  extensively  used 
in  this  country  to-day.  It  is  constructed  of  brick  and,  as  its 
name  implies,  has  the  form  of  a  beehive.  Bituminous  coal  is 
placed  in  this  oven  or  kiln  and  a  part  of  it  burned  in  order  to 
carbonize  the  remainder,  while  the  volatile  products,  such  as 
gas,  ammonia,  and  tar,  are  allowed  to  escape  through  an  open- 
ing in  the  top  of  the  kiln  where  they  are  lost  in  flame  and  smoke. 
Coke  ovens  in  which  the  by-products  are  saved  are  now  used 
to  some  extent  in  this  country,  and  sooner  or  later  will  un- 
doubtedly replace  the  old-style  oven  entirely,  and  thus  increase 
our  output  of  tar  enormously." 

Water-Gas  Tar.f  "The  manufacture  of  water  gas  depends 
upon  the  reaction  between  water  vapor  and  incandescent  carbon. 
The  result  of  this  reaction  is  what  is  known  as  water  or  blue 
gas,  composed  of  about  equal  parts  of  hydrogen  and  carbon 
monoxide.  This  gas  has  a  heating  value  of  about  300  B.  T.  U. 
per  cubic  foot,  but  it  is  non-luminous,  so  that  for  use  in  the 
open-flame  burners  it  has  to  be  enriched  by  the  addition  of 
some  hydrocarbon.  Water  gas  as  we  now  know  it  is  manu- 
factured in  an  internally  fired  generator  and  the  enriching  hydro- 
carbon is  added  in  the  form  of  oil  in  vessels  called  respectively 
the  carbureter  and  the  superheater. 

"When  the  tar  which  leaves  the  generating  apparatus  in 
the  form  of  a  vapor  comes  in  contact  with  the  water  in  the 
wash  box  of  the  machine,  the  greater  portion  is  condensed. 
Some  of  it,  however,  remains  in  the  form  of  mist,  which  is 

*  See  Circular  97,  U.  S.  Office  of  Public  Roads,  "Coke-Oven  Tars  of  the 
United  States,"  by  Prevost  Hubbard. 

fSee  1912-1913  Lecture  by  W.  H.  Fulweiler,  Chief  Chemist,  United  Gas 
Improvement  Company,  on  "The  Manufacture  of  Refined  Water-Gas  Tar," 
in  the  Graduate  Course  in  Highway  Engineering  at  Columbia  University. 


210  ELEMENTS   OF  HIGHWAY   ENGINEERING 

removed  from  the  gas  in  the  condensers  and  tar  extractors, 
along  with  a  considerable  portion  of  the  excess  steam  in  the 
water  gas.  Owing  to  the  low  gravity  of  the  crude  tar,  it  does  not 
immediately  separate  from  the  water  and  is,  therefore,  passed 
through  tanks  provided  with  baffling  plates  where  it  is  par- 
tially separated  from  the  water.  It  is  then  stored  in  large  tanks, 
where  under  the  influence  of  gravity  the  tar  gradually  rises  to 
the  surface,  practically  free  from  water. 

"The  water-gas  tar  is  charged  into  a  fire  still,  and  the  dis- 
tillation commenced.  The  first  fraction  cut  is  known  as  light 
oil,  and  has  a  gravity  of  0.953,  tnen  comes  the  naphthalene 
oil  of  about  0.990.  The  next  fraction  cut  is  dead  oil,  which 
has  a  gravity  of  about  i.oi,  and  following  this  comes  creosoting 
oil,  with  a  gravity  of  about  1.05.  The  distillation  is  finished  at 
the  end  of  the  creosoting  oil  cut.  The  residue  remaining  in  the 
still  is  either  road  tar  or  a  pitch,  depending  upon  the  tempera- 
ture at  which  the  distillation  ceases.  Varying  grades  of  road 
tar  or  pitch  result,  according  to  the  temperature  at  which  dis- 
tillation ceases.  The  higher  the  distillation  temperature,  of 
course,  the  harder  the  grade  of  pitch  will  be  made. 

"The  road  compound  as  it  comes  from  the  stills  is  run  off 
into  closed  coolers,  where  its  temperature  is  reduced,  and  is 
then  combined  with  the  required  amount  of  asphalt  or  heavy 
oil,  according  to  the  grade  of  material  that  is  being  made.  In 
all  this  work  the  material  is  handled  by  what  are  known  as 
blow  cases,  in  which  compressed  air  is  the  actuating  medium 
instead  of  pumps.  The  mixing  is  done  by  an  especially  arranged 
series  of  nozzles  operated  with  compressed  air." 

TESTS  AND  SPECIFICATIONS  FOR  PHYSICAL  AND  CHEMICAL 

PROPERTIES 

Various  tests  have  been  devised  in  order  to  determine  the 
physical  and  chemical  properties  of  bituminous  materials.  Tests 
are  made  for  control  of  the  manufacture  of  bituminous  materials, 
to  obtain  a  record  of  the  properties  of  materials  used,  and  are 
employed  in  specifications  to  secure  the  materials  desired  for 


BITUMINOUS    MATERIALS  211 

t 

use  in  the  construction  and  maintenance  of  road*  and  pave- 
ments. In  this  chapter  the  typical  tests  used  are  mentioned  or 
explained  and  brief  interpretations  of  the  results  of  such  tests 
are  given. 

LISTS  OF  TESTS.  It  is  desirable  in  connection  with  inves- 
tigations covering  service  tests  of  bituminous  materials  to  be 
used  in  the  construction  of  various  types  of  surfaces  and  pave- 
ments to  have  at  hand  a  complete  record  of  the  chemical  and 
physical  properties  of  the  materials.  For  such  purposes  the 
Special  Committee  on  "Materials  for  Road  Construction"  of 
the  American  Society  of  Civil  Engineers,  in  its  1915  Report, 
recommended  the  adoption  of  the  following  lists  of  tests,  as 
including  all  those  probably  of  value  in  determining  and  record- 
ing the  characteristics  of  the  bituminous  materials  used  in  this 
connection : 
Tars. 

Specific  gravity  at  25°  C.  (77°  F.). 

Flash  point. 

Solubility  in  CS2  (carbon  disulphide). 

Consistency  at  4°  C.   (39°  F.),  25°  C.   (77°  F.),  46°  C. 

(115°  F.),  98°  C.  (208°  F.). 
Melting  point. 
Loss  on  evaporation  at  163°  C.  (325°  F.). 

Consistency  of  residue  at  4°  C.  (39°  F.),  25°  C.  (77°  F.), 

46°  C.  (115°  F.),  98°  C.  (208°  F.). 
Melting  point  of  residue. 
Distillation. 

Consistency  of  residue  at  4°  C.  (39°  F.),  25°  C.  (77°  F.), 

46°  C.  (115°  F.),  98°  C.  (208°  F.). 
Melting  point  of  residue. 
Asphaltic  Materials. 

Specific  gravity  at  25°  C.  (77°  F.). 
Flash  point. 

Solubility  in  CS2  (carbon  disulphide). 
Solubility  of  bitumen  in  CCU  (carbon  tetrachloride) . 
Solubility  of  bitumen  in  petroleum  naphtha. 
Character  of  residue  on  glass. 


212  ELEMENTS   OF   HIGHWAY   ENGINEERING 

Consistency  at  4°  C.   (39°  F.),  25°  C.   (77°  F.),  46°  C. 
(115°  F.),  98°  C.  (208°  F.). 

Melting  point. 

Ductility  at  4°  C.  (39°  F.),  and  25°  C.  (77°  F.). 

Fixed  carbon  content. 

Paraffin  content. 

Loss  on  evaporation  at  163°  C.  (325°  F.). 

Consistency  of  residue  at  4°  C.  (39°  F.),  25°  C.  (77°  F.), 

46°  C.  (115°  F.).  : 
Melting  point  of  residue. 

Ductility  of  residue  at  4°  C.  (39°  F.),  and  25°  C.  (77°  F.). 
The  tests  used  in  a  given  specification  depend  upon  the  kind  of 
bituminous  material  employed  and  the  method  used.  For  ex- 
ample, a  specification  for  a  refined  tar  to  be  used  as  a  bituminous 
cement  in  a  bituminous  concrete  pavement  in  which  the  aggre- 
gate consists  of  broken  stone  composing  one  product  of  a  stone- 
crushing  plant,  would  include  reference  to  tests  for  specific 
gravity,  solubility  in  carbon  disulphide,  consistency  with  the 
New  York  Testing  Laboratory  float  apparatus  or  with  a  pene- 
trometer,  melting  point,  distillation,  specific  gravity  of  total 
distillate  and  melting  point  of  pitch  residue  remaining  after 
distillation.  In  the  case  of  an  asphalt  cement  to  be  used  in 
the  above  type  of  construction,  the  tests  referred  to  in  the 
specifications  would  include  specific  gravity,  flash  point,  pene- 
tration at4°C.,  25°C,  and  46°  C.,  melting  point  or  consistency 
with  the  New  York  Testing  Laboratory  float  apparatus,  loss 
on  evaporation  at  163°  C.  and  penetration  of  the  residue  from 
evaporation,  solubility  in  carbon  disulphide,  solubility  of  bitumen 
in  carbon  tetrachloride,  solubility  of  bitumen  in  paraffin  naphtha, 
and  fixed  carbon. 

For  the  purposes  of  this  chapter  it  is  not  necessary  to  de- 
scribe tests,  the  names  of  which  give  an  indication  of  the  method 
of  performing  the  tests.  Such  tests  as  specific  gravity,  solubility 
in  carbon  disulphide,  carbon  tetrachloride,  petroleum  naphtha, 
evaporation,  and  distillation  will,  therefore,  not  be  described. 
Brief  explanations  of  the  other  tests  included  in  the  above  lists 
will  be  given.  Detailed  descriptions  of  methods  of  conducting 


BITUMINOUS   MATERIALS  213 

all  of  the  tests  for  tars  and  asphaltic  materials  covered  by  the 
above  lists  are  given  in  Appendix  II. 

Flash  Point.  The  material  is  placed  in  a  cup  fitted  with  a 
glass  cover  having  a  small  opening.  The  temperature  of  the 
material  is  raised  and  a  testing  flame  is  inserted  in  the  opening 
of  the  cover  from  time  to  time.  The  appearance,  for  a  few 
seconds,  of  a  faint  bluish  flame  over  the  entire  surface  of  the 
bituminous  material  will  show  that  the  flash  point  has  been 
reached  and  the  temperature  at  this  point  is  recorded. 

Melting  Point.  The  material  is  melted  and  molded  into  a 
J^-inch  cube.  The  cube  is  placed  on  a  wire  and  suspended 
one  inch  above  the  bottom  of  a  beaker.  The  temperature 
of  the  cube  is  then  raised  until  the  material  softens  and 
touches  the  bottom  of  the  beaker.  The  temperature  at  this 
point  of  the  operation  is  considered  the  melting  point  of  the 
material. 

Consistency.  The  consistency  of  bituminous  materials  is 
determined  by  the  Engler  viscosimeter,  the  New  York  Testing 
Laboratory  float  apparatus,  or  the  penetrometer. 

With  the  Engler  Viscosimeter  the  viscosity  of  liquid  bituminous 
materials  is  determined  by  noting  the  time  which  is  required 
for  a  given  amount  of  the  material,  having  a  given  temperature, 
to  flow  through  a  very  small  orifice.  The  result  of  the  test 
should  be  expressed  as  specific  viscosity,  which  equals  the  ratio 
of  the  number  of  seconds  required  for  the  passage  of  a  given 
volume  of  the  bituminous  material  at  the  temperature  used 
divided  by  the  number  of  seconds  required  for  the  passage  of 
the  same  volume  of  water  at  25°  C.  (77°  F.). 

The  New  York  Testing  Laboratory  Float  Apparatus  consists 
of  an  aluminum  float  and  a  brass  collar.  The  collar  is  filled  with 
bituminous  material  and  screwed  in  to  the  bottom  of  the  aluminum 
float  and  the  apparatus  placed  on  the  surface  of  a  water  bath. 
As  the  plug  of  bituminous  material  in  the  collar  becomes  warm 
and  fluid,  due  to  the  heat  from  the  water  bath  which  is  main- 
tained at  any  temperature  desired  for  the  test,  it  is  gradually 
forced  upward  and  out  of  the  collar  until  water  gains  entrance 
to  the  saucer  and  causes  it  to  sink.  The  time  in  seconds  be- 


214  ELEMENTS   OF  HIGHWAY   ENGINEERING 

tween  placing  the  apparatus  on  the  water  and  when  the  float 
sinks  is  taken  as  the  measure  of  consistency. 

The  Penetration  Test  is  made  by  measuring  the  distance  a 
weighted  standard  needle  will  penetrate  into  the  material  at  a 
given  temperature  in  a  given  period  of  time.  The  temperatures, 
weights,  and  periods  of  time  which  are  employed  to  a  considerable 
extent  are  as  follows:  penetration  at  4°  C.  with  a  weight  of 
200  grams  for  i  minute;  penetration  at  25°  C.  with  a  weight  of 
100  grams  for  5  seconds;  penetration  at  46°  C.  with  a  weight 
of  50  grams  for  5  seconds.  When  the  penetration  of  a  material 
is  mentioned  without  reference  to  temperature,  weight  of  the 
load,  or  time,  it  is  understood  that  reference  is  made  to  the 
penetration  at  the  normal  temperature  of  25°  C.  (77°  F.)  with 
a  weight  of  100  grams  for  5  seconds.  The  unit  of  penetration 
is  o.i  mm.  In  literature  and  specifications  the  penetration  is 
referred  to  in  terms  of  the  above  unit  either  as  a  penetration 
of  6.4  mm.  or  64. 

Ductility.  In  the  ductility  test  a  briquette  of  the  material 
is  formed  in  a  standard  briquette  mold.  The  briquette  with 
clips  attached  is  placed  in  a  ductility  testing  machine  filled 
with  water  at  a  temperature  of  4°  C.  or  25°  C.  The  briquette 
is  then  pulled  apart  at  a  uniform  rate  and  the  distance  in  centi- 
meters registered  at  the  time  of  rupture  of  the  thread  of  bitu- 
minous material  is  taken  as  the  measure  of  ductility. 

Fixed  Carbon.  Fixed  carbon  is  the  organic  matter  of  the 
residual  coke  obtained  upon  burning  hydrocarbon  products  in 
a  covered  vessel  in  the  absence  of  free  oxygen. 

Paraffin.  The  percentage  of  paraffin  in  a  bituminous  mate- 
rial is  determined  by  a  somewhat  complex  chemical  test,  which 
is  fully  described  in  Appendix  II. 

INTERPRETATION  OF  RESULTS  OF  TESTS.  Unless  otherwise 
stated  the  quoted  interpretations  of  the  results  of  tests  are  by 
Prevost  Hubbard,*  being  abstracts  from  a  "Communication" 
on  the  subject,  "Various  Materials  in  Use  for  the  Purposes  of 

*  Chemical  Engineer,  U.  S.  Office  of  Public  Roads  and  Rural  Engineering, 
and  Lecturer  in  Highway  Engineering  Chemistry,  Graduate  Course  in  High- 
way Engineering,  Columbia  University. 


BITUMINOUS   MATERIALS  215 

Construction  and  Maintenance;  Conditions  to  .be  Fulfilled; 
Tests;  Units  to  be  Adopted,"  which  was  presented  for  the 
United  States  to  the  Second  International  Road  Congress. 

Specific  Gravity.  "It  is  of  value  mainly  as  a  means  of 
identification,  but  when  considered  in  connection  with  other 
tests  is  often  of  service  in  determining  the  suitability  of  the 
material  for  road  purposes.  As  applied  to  oil  and  oil  products, 
the  specific  gravity  is  a  rough  indication  of  the  amount  of  heavy 
hydrocarbons  which  give  body  to  the  material.  Crude  petro- 
leums vary  in  specific  gravity  from  0.73  to  0.98  and  slightly 
higher,  paraffin  oils  as  a  rule  having  the  lowest  specific  gravity 
and  asphaltic  oils  the  highest.  The  former  have  practically  no 
value  for  road  work,  while  the  latter  constitute  the  most  de- 
sirable type.  Oils  containing  a  semi-asphaltic  base  hold  an 
intermediate  position  and  will  usually  run  higher  in  specific 
gravity  than  the  paraffin  oils  and  lower  than  the  truly  asphal- 
tic oils. 

"Crude  coal  tars  vary  in  specific  gravity  from  i.o  to  1.22 
and  sometimes  higher,  while  crude  water-gas  tars  lie  between 
i.oo  and  i.io.  In  coal  tars,  the  specific  gravity  is  largely  de- 
pendent upon  the  percentage  of  free  carbon  or  soot  which  it 
contains,  those  of  low  specific  gravity  holding  but  little  and  those 
of  high  specific  gravity  holding  a  large  amount  of  free  carbon. 
Thus  a  crude  tar  having  a  specific  gravity  of  less  than  1.15  will 
usually  show  less  than  12  percent  free  carbon,  while  those 
running  as  high  as  1.22  will  have  30  percent  and  over.  In 
refined  tars  specific  gravity  naturally  increases  with  consistency, 
both  because  the  lighter  hydrocarbons  and  water  have  been 
removed  and  because  the  relative  proportion  of  free  carbon 
has  been  increased  in  the  residue.  In  such  products  for  a  given 
consistency  a  low  specific  gravity  is  to  be  preferred  to  a  high 
one.  This  is  not  true,  however,  when  considering  refined  products 
of  different  consistencies,  as  in  such  cases,  while  the  percentage 
of  free  carbon  might  be  the  same,  the  most  desirable  product 
might  show  the  highest  specific  gravity  for  the  reasons  mentioned 
above." 

Flash  Point.     "This   determination  is  of  little  value  other 


216  ELEMENTS   OF  HIGHWAY   ENGINEERING 

than  as  a  quick  means  of  differentiating  between  the  heavy 
crude  oils  and  cut-back  products  and  the  fluid  residuums,  al- 
though it  also  indicates  the  point  to  which  a  refined  oil  has 
been  distilled.  Crude  oils  have,  of  course,  a  lower  flash  point 
than  residual  oils,  and  among  the  crude  oils  themselves  those 
of  a  paraffin  nature  usually  flash  at  a.  lower  temperature  than 
the  asphaltic.  The  former  may  run  as  low  as  ordinary  tem- 
perature, while  the  latter  are  sometimes  as  high  as  135°  C. 
Some  crude  asphaltic  oils  will,  however,  show  quite  as  low  flash 
point  as  the  paraffin  oils,  so  that  no  great  dependence  can  be 
placed  upon  this  difference  in  crude  petroleums.  The  flash  point 
of  residual  road  oils  commonly  exceeds  200°  C.,  while  that  of 
cut-back  products  will  vary  greatly,  according  to  the  flash  point 
of  the  flux  and  the  percentage  and  character  of  the  heavier 
residual  product.  Thus,  in  a  certain  instance,  when  90  percent 
of  a  distillate  having  a  flash  point  of  100°  C.  was  mixed  with 
10  percent  of  an  oil  asphalt  having  a  flash  point  of  260°  C., 
the  flash  point  of  the  resulting  mixture  was  raised  to  143°  C., 
and  the  addition  of  60  percent  of  the  heavier  product  only 
increased  this  temperature  by  5  degrees.  Great  care  should,  of 
course,  be  taken  when  heating  low  flash  point  oils  in  an  open 
kettle  or  tank  that  the  oil  does  not  catch  fire.  Such  oils,  how- 
ever, rarely  require  heating  before  application,  as  they  are  usually 
quite  fluid  when  cold." 

Melting  Point.  "A  determination  of  the  melting  point  of 
solid  bitumens  is  mainly  of  value  as  a  means  of  identification 
and  for  control  work  on  the  part  of  manufacturers.  The  melting 
point  of  a  bitumen  is  directly  related  to  its  hardness  and  brittle- 
ness,  but  the  relations  are  not  the  same  for  all  classes.  Thus, 
at  normal  temperature,  a  blown  oil  with  a  melting  point  of 
50°  C.  is  neither  hard  nor  brittle,  while  a  tar  pitch  is  both. 
As  the  melting  point  rises,  however,  they  both  become  harder 
and  more  brittle.  The  climate  under  which  a  bitumen  is  to 
serve  as  a  road  binder  should  be  considered  in  connection  with 
its  melting  point,  and  this  is  particularly  true  of  tar  products." 

Consistency.  Maximum  and  minimum  limits  covering  con- 
sistency are  essential  parts  of  all  specifications  for  bituminous 


BITUMINOUS   MATERIALS  217 

materials.  Such  limitations  are  of  particular  value  since  it  is 
possible  by  their  use  to  secure  the  grade  of  a  given  type 
of  bituminous  material  which  is  most  suitable  for  any 
method  of  use,  and,  furthermore,  because  it  is  practicable  thus 
to  ensure  reasonable  uniformity  in  the  consistency  of  the 
bituminous  material  supplied  for  a  given  piece  of  work.  It  is 
apparent  that  the  range  in  limits  should  be  as  narrow  as  the 
practicable  manufacture  of  the  bituminous  materials  will  permit. 

The  utilization  of  the  various  standard  methods  employed 
for  the  determination  of  consistency,  that  is,  with  the  Engler 
Viscosimeter,  the  New  York  Testing  Laboratory  Float  Apparatus, 
and  the  penetrometer,  depends  upon  the  characteristics  of  the 
materials.  For  example,  the  Engler  Viscosimeter  is  generally 
employed  to  determine  the  consistency  of  liquid  bituminous 
materials;  the  New  York  Testing  Laboratory  Float  Test  for 
the  determination  of  the  consistency  of  semi-solid  and  solid 
tars  and  pitches;  and  in  most  cases  the  penetrometer  for  the 
determination  of  the  consistency  of  semi-solid  and  solid  asphaltic 
materials.  " Penetration  determinations  are  seldom  made  upon 
tars  because  their  surface  tension  is  so  high  that  even  approxi- 
mately correct  penetrations  cannot  be  recorded  and  the  presence 
of  free  carbon  in  varying  quantities  affects  the  results  very 
considerably."  In  order  to  show  the  methods  of  stating  con- 
sistency and  the  variations  in  consistency  of  a  given  type  of 
material  dependent  upon  its  use,  the  following  examples  are  given : 

Coal-Gas  Tar  for  Cold  Application  to  Broken  Stone  and  Gravel 
Roads.  When  tested  by  means  of  the  Engler  Viscosimeter  at 
40°  C.  (104°  F.)  the  specific  viscosity  of  the  first  50  cc.  passing 
the  orifice  of  the  viscosimeter  shall  be  not  less  than  8  nor  more 
than  13. 

Coal-Gas  Tar  for  the  Construction  of  Bituminous  Surfaces  on 
Broken  Stone  and  Gravel  Roads.  When  tested  by  means  of  the 
New  York  Testing  Laboratory  Float  Apparatus,  the  float  shall 
not  sink  in  water  maintained  at  50°  C.  (122°  F.)  in  less  than 
40  seconds  nor  more  than  100  seconds. 

Coal-Gas-  Tar  Cement  for  Use  in  the  Construction  of  Bituminous 
Macadam  Pavements.  When  tested  by  means  of  the  New  York 


218  ELEMENTS   OF  HIGHWAY  ENGINEERING 

Testing  Laboratory  Float  Apparatus,  the  float  shall  not  sink 
in  water  maintained  at  50°  C.  (122°  F.)  in  less  than  150  seconds 
nor  more  than  180  seconds. 

Asphalt  Cement  (one  type).  When  tested  with  a  standard 
No.  2  needle  by  means  of  a  Dow  Penetrometer  (or  other  pene- 
trometer  giving  the  same  results  as  the  Dow  machine),  it  shall 
show  penetrations  within  the  following  limits  for  the  conditions 
stated. 

For  Use  in  the  Construction  of  Bituminous  Macadam  Pave- 
ments: loo-gram  load,  5  seconds,  at  25°  C.  (77°  F.),  from  100 
to  120;  2oo-gram  load,  i  minute,  at  4°  C.  (39°  F.),  not  less 
than  50. 

For  Use  in  the  Construction  of  Bituminous  Concrete  Pavements 
Having  an  Aggregate  Composed  of  One  Product  of  a  Stone-Crushing 
Plant  Varying  in  Size  from  yi  to  1^4  Inches:  loo-gram  load, 
5  seconds,  at  25°  C.  (77°  F.),  from  75  to  90;  2oo-gram  load, 
i  minute,  at  4°  C.  (39°  F.),  not  less  than  35;  5o-gram  load, 
5  seconds,  at  46°  C.  (115°  F.),  not  more  than  250. 

For  Use  in  the  Construction  of  Sheet  Asphalt  Pavements:  100- 
gram  load,  5  seconds,  at  25°  C.  (77°  F.),  from  65  to  75;  200- 
gram  load,  i  minute,  at  4°  C.  (39°  F.),  not  less  than  35;  50-gram 
load,  5  seconds,  at  46°  C.  (115°  F.),  not  more  than  250. 

For  Use  as  Filler  in  Brick  and  Stone  Block  Pavements:  100- 
gram  load,  5  seconds,  at  25°  C.  (77°  F.),  from  30  to  40;  200- 
gram  load,  i  minute,  at  4°  C.  (39°  F.),  not  less  than  18;  5o-gram 
load,  5  seconds,  at  46°  C.  (115°  F.),  not  more  than  70. 

Distillation.  "The  distillation  test  as  applied  to  tars  is  a 
very  valuable  one,  both  for  the  purpose  of  ascertaining  their 
road-building  properties  and  method  of  preparation  if  they  are 
refined  products.  All  crude  tars  contain  water  which,  of  course, 
appears  in  the  first  fraction  to  110°  C.  In  coal  tars  this  water 
is  ammoniacal,  while  in  water-gas  tars  it  is  not.  No  tar  con- 
taining water  should  be  employed  as  a  permanent  binder,  and 
even  in  temporary  binders  its  presence  is  detrimental." 

Solubility  in  Carbon  Disulphide.  "For  practical  purposes 
all  organic  matter  soluble  in  cold  carbon  disulphide  is  considered 
as  bitumen.  Fluid  oils  are  almost  completely  soluble  in  this  ma- 


BITUMINOUS   MATERIALS  219 

terial,  and  also  blown  oils  and  oil  pitches,  unless  they  have  been 
cracked  to  the  point  of  producing  free  carbon.  The  solubility 
of  the  bitumen  itself  is  entirely  independent  of  its  character  and 
consistency,  so  that  the  amount  and  character  of  insoluble  mate- 
rial are  of  most  interest  in  this  test.  This  material  is  of  no 
value  from  the  standpoint  of  road  work,  but  indicates  whether 
an  asphalt  has  been  employed  in  the  preparation  of  the  binder, 
also  whether  a  product  has  been  destructively  distilled  during 
its  preparation,  the  determining  factor  in  the  former  case  being 
the  amount  of  mineral  matter  present  and  the  amount  of  organic 
material  in  the  absence  of  mineral  matter  in  the  latter  case. 
It  is,  of  course,  possible  to  adulterate  a  preparation  so  as  to 
give  misleading  results,  unless  the  analyst  is  familiar  with  the 
characteristics  which  the  addition  of  various  solid  native  bitu- 
mens will  produce  in  oils  of  different  types. 

"Tars,  with  the  exception  of  those  produced  in  blast  fur- 
naces, contain  only  a  small  fraction  of  one  percent  mineral 
matter.  Practically  all  material  insoluble  in  carbon  disulphide 
is,  therefore,  organic  material,  commonly  known  as  free  carbon. 
Water-gas  tars  or  oil  tars  as  they  are  often  called  will  usually 
contain  less  than  this  amount  even  when  refined  to  a  specific 
gravity  of  1.17,  and  crude  water-gas  tar  seldom  exceeds  2  per- 
cent free  carbon.  Most  crude  coke-oven  tars  will  carry  from 
4  to  10  percent  free  carbon,  unless  they  have  been  produced  at 
very  high  temperatures,  while  the  modern  gas-house  coal  tars 
rarely  show  less  than  15  percent  and  sometimes  run  as  high  as 
30  percent  and  over." 

Solubility  in  88  Degree  Baume  Naphtha.  "As  applied  to 
oils  and  oil  products,  this  determination  is  of  value  as  indicating 
the  amount  of  body-forming  hydrocarbons  which  give  mechanical 
stability  to  the  material.  No  oils  carrying  less  than  4  percent 
naphtha-insoluble  bitumen  will  prove  of  service  other  than  as 
dust  preventives.  Crude  paraffin  oils  are  almost  entirely  dis- 
solved by  this  solvent,  while  the  asphaltic  oils  contain  very 
appreciable  amounts  of  naphtha-insoluble  bitumen.  Residual 
oils  carry  larger  quantities  than  the  crude  oils  from  which  they 
are  produced,  and  blown  oils  in  particular  show  very  high  per- 


220  ELEMENTS   OF  HIGHWAY  ENGINEERING 

centages  of  insoluble  hydrocarbons,  sometimes  running  as  high 
as  25  or  30  percent.  In  this  type  of  oil  the  naphtha-insoluble 
bitumen  increases  with  the  amount  of  blowing  to  which  the  oil 
has  been  subjected. 

"Asphaltic  cements  containing  appreciable  quantities  of  these 
solid  products  will  necessarily  show  relatively  high  percentages 
of  bitumen  insoluble  in  naphtha.  While  the  binding  value  of 
asphaltic  oils  and  cements  is  undoubtedly  dependent  upon  the 
presence  of  the  naphtha-insoluble  hydrocarbons,  variations  in 
the  character  of  these  hydrocarbons  exert  a  marked  influence 
upon  the  characteristics  of  the  original  material.  Bitumens  in- 
soluble in  naphtha  are  commonly  known  as  asphaltenes,  while 
those  soluble  are  called  malthenes.  It  should  be  understood, 
however,  that  both  terms  cover  a  multitude  of  hydrocarbons 
which  vary  greatly  among  themselves.  The  character  of  the 
naphtha-soluble  bitumen  is  of  interest  from  the  standpoint  of 
road  treatment,  that  which  is  sticky  after  the  solvent  has  been 
evaporated  indicating  better  road-building  qualities  in  the  original 
material  than  that  which  is  greasy." 

Evaporation.  "  This  test  is  a  purely  arbitrary  one,  but  when 
applied  to  road  oils  will  often  prove  of  considerable  value.  It 
is  believed  that  the  loss  in  weight  thus  produced  is  a  fair  com- 
parative indication  of  loss  by  volatilization  suffered  by  the  mate- 
rial in  the  course  of  time  when  applied  to  the  road,  also  that 
the  character  of  the  residue  is  similar  to  that  eventually  left 
in  the  road.  A  determination  of  the  consistency  of  this  residue 
should,  if  possible,  be  made,  and  particular  attention  paid  as 
to  whether  it  is  of  a  greasy  or  sticky  nature.  The  volatilization 
test  is  not  a  quantitative  determination  of  any  one  class  of 
volatile  oils  present  in  the  original  material,  but  only  of  its 
tendency  to  give  up  these  volatile  oils.  If  the  material  has  a 
certain  consistency  which  it  is  desired  to  maintain  after  appli- 
cation, it  should  show  a  low  volatilization  and  should  not  be 
subject  to  hardening  by  oxidation  or  other  causes.  A  deter- 
mination of  penetration  of  the  residue  as  compared  with  that 
of  the  original  material  is  of  value  in  determining  this  fact. 
A  material  which  must  be  soft  and  sometimes  fluid  on  account 


BITUMINOUS   MATERIALS  221 

of  the  desired  method  of  application  and  character  of  the  road 
treated,  should  very  properly  suffer  high  loss  by  volatilization 
in  order  that  it  may  be  capable  of  attaining  proper  consistency 
under  service  conditions. 

"  Fluid  products  to  be  used  in  the  surface  treatment  of  roads 
need  not  necessarily  show  a  high  loss  by  volatilization  nor  a 
great  increase  in  the  consistency  of  their  residues,  although  the 
latter  is  a  desirable  property.  They  are  mainly  of  value  as 
dust  preventives  and  binders  for  the  thin  coat  of  fine  material 
upon  the  road  surface  and  cannot  affect  the  character  of  the 
road  proper  unless  applied  in  large  quantities.*  If  their  residues 
are  not  of  a  sticky  nature,  they  will,  however,  produce  an  un- 
desirable surface  condition  in  wet  weather  unless  applied  in 
very  small  quantities.  In  general,  all  residues  should  be  sticky 
or  adhesive,  as  otherwise  they  will  act  more  as  lubricants  than 
as  road  binders.  A  paraffin  oil  will  produce  a  greasy  residue; 
an  asphaltic  oil  will  produce  one  that  is  sticky.  While  the  latter 
may  be  successfully  employed  in  road-work,  the  former  is 
worthless  for  this  purpose. 

"  In  certain  instances,  determinations  of  the  so-called  asphalt 
contents  of  oils  have  been  made  by  driving  off  volatiles  until 
the  residue  is  of  a  certain  consistency.  To  produce  this  residue, 
it  is  often  necessary  to  subject  the  bitumen  to  such  high  tem- 
peratures that  chemical  changes  take  place  which  would  never 
occur  under  service  conditions.  For  this  reason  the  test  is  not 
a  determination  of  the  actual  asphalt  contents,  but  only  of  the 
ability  of  the  oil  to  produce  an  asphaltic  base  of  given  con- 
sistency under  the  action  of  high  temperatures.  Such  a  test 
is,  therefore,  misleading  and  has  resulted  in  much  confusion 
among  road  engineers  as  to  the  relative  binding  value  of  oils." 

Fixed  Carbon.  "  The  fixed  carbon  determination  shows  much 
the  same  thing  as  that  for  naphtha-insoluble  bitumen,  as  it 
serves  as  an  indication  of  the  mechanical  stability  of  an  oil. 
Paraffin  oils  show  but  little  fixed  carbon,  while  the  asphaltic 
oils  run  higher  and  the  asphalts  still  higher.  The  terms  '  fixed 
carbon '  and  '  free  carbon '  should  not  be  confused,  as  they  have 
entirely  different  meanings.  Free  carbon  always  exists  as  such 


222  ELEMENTS   OF   HIGHWAY   ENGINEERING 

in  the  material,  while  fixed  carbon  is  the  coke  resulting  from 
the  ignition  of  the  bitumen  in  the  absence  of  oxygen.  Fixed 
carbon  determinations  are  seldom  made  upon  tars,  as  the  presence 
of  free  carbon  interferes  with  this  test.  Owing  to  a  miscon- 
ception as  to  what  fixed  carbon  represents,  specifications  have 
sometimes  been  made  limiting  the  percentage  of  this  substance 
to  a  very  low  figure.  Providing  that  free  carbon  is  absent, 
comparatively  high  percentages  of  fixed  carbon  are  a  rather 
desirable  property  in  oils,  for  the  reason  mentioned,  especially 
if  they  are  to  be  used  in  construction  work." 

Paraffin.  Interpretation  of  Test  by  A.  W.  Dow,  M.  Am. 
Inst.  Chem.  E.,  and  Francis  P.  Smith,  M.  Am.  Soc.  C.  E.* 
"  We  are  decidedly  of  the  opinion  that  the  scale  paraffin  test 
per  se  should  not  be  regarded  as  a  measure  of  value  of  bituminous 
compounds  for  road-making  or  paving  purposes: 

"(i)  Because  there  is  no  evidence  to  show  that  the  finding  of 
scale  paraffin  by  the  modified  Holde  method,  in  which  the  mate- 
rial under  examination  is  first  distilled  in  the  laboratory,  is 
proof  that  scale  paraffin  or  any  detrimental  form  of  paraffin  is 
present  in  the  bituminous  material. 

"(2)  Because  there  is  no  evidence  to  prove  that  paraffin  of 
any  kind  is  a  deleterious  constituent  for  a  bituminous-road 
cement." 

UTILIZATION  OF  TESTS  IN  SPECIFICATIONS.!  "  The  ultimate 
utilization  of  tests  for  the  purpose  of  selecting  material  for  a 
given  use  makes  it  necessary  that  (i)  the  test  limits  adopted 
shall  specifically  define  the  material,  and  (2)  that  the  material 
thus  defined  shall  have  previously  proved  satisfactory  for  that 
particular  use. 

"  The  individual  tests  required  by  specifications  for  bitumi- 
nous road  and  paving  materials  may  serve  one  or  more  of  the 
three  following  purposes: 

*  See  Engineering  News,  June  8,  1911,  pages  680-683. 

f  By  Prevost  Hubbard,  Chemical  Engineer,  U.  S.  Office  of  Public  Roads 
and  Rural  Engineering  and  Lecturer  in  Highway  Engineering  Chemistry, 
Graduate  Course  in  Highway  Engineering,  Columbia  University,  1913 
Proceedings,  American  Road  Builders'  Association,  pages  213-216. 


BITUMINOUS   MATERIALS  223 

"  (i)  They  may  directly  indicate  the  suitability  for  a  given 
use  of  the  material  specified. 

"  (2)  They  may  serve  as  a  means  of  identifying  the  source  of 
a  material,  or  even  the  material  itself. 

"  (3)  They  may  serve  to  control  uniformity  in  the  prepara- 
tion or  manufacture  of  a  material. 

"  The  first  of  these  purposes  is  undoubtedly  the  most  im- 
portant and  is  usually  the  only  one  considered  by  the  lay  mind. 
In  the  case  of  bituminous  materials,  this  purpose  is  only  partly 
accomplished  by  a  comparatively  few  tests.  As  examples,  may 
be  mentioned  tests  of  consistency,  such  as  the  penetration  test, 
the  float  test,  and  the  test  for  viscosity.  Such  tests  can  only 
be  of  maximum  value,  however,  when  applied  to  a  specific  type 
of  bituminous  material  and  when  considered  in  connection  with 
other  tests  which,  by  themselves,  may  not  directly  indicate 
suitability.  Thus,  for  a  certain  type  of  bituminous  concrete 
pavement  the  proper  penetration  limits  at  25°  C.  for  a  Cali- 
fornia asphalt  may  lie  between  7.0  and  9.0  millimeters,  while 
the  proper  penetration  limits  for  a  fluxed  Bermudez  asphalt  to 
be  used  in  exactly  the  same  type  of  pavement  and  under  the 
same  conditions,  may  be  entirely  different,  say,  from  14.0  to 
1 6.0  millimeters.  It  is  evident  that  to  attempt  to  cover  the 
penetration  limits  for  both  materials  under  one  specification 
would  be  useless.  In  the  first  place,  such  test  limits  as  7.0  to 
16.0  millimeters  are  so  wide  as  to  insure  but  little  uniformity 
in  different  lots  of  the  same  material;  and  in  the  second  place, 
an  entirely  unsuitable  material  of  one  class  might  be  supplied 
under  the  maximum  test  limit  of  the  other  class.  The  fallacy 
of  blanket  specifications,  which  have  already  been  advocated 
to  a  considerable  extent,  is  thus  easily  demonstrated. 

"If  a  penetration  test  is  essential  under  the  conditions  just 
mentioned,  it  is  apparent  that  recourse  must  be  had  to  separate 
type  specifications ;  and  if  this  is  so  the  specifications  must 
contain  either  tests  or  test  limits  which  will  describe  certain 
peculiarities  of  the  type  specified,  that  are  not  common  to  other 
types.  In  many  cases  this  cannot  be  done  by  means  of  a  single 
test  and  two  or  more  such  tests  will  be  required. 


224  ELEMENTS   OF  HIGHWAY  ENGINEERING 

"This  brings  us  to  a  consideration  of  the  second  purpose 
previously  mentioned,  i.  e.,  the  use  of  tests  as  a  means  of  identi- 
fication. There  are  a  number  of  such  tests,  among  which  may 
be  mentioned  specific  gravity,  melting  point,  solubility  in  carbon 
disulphide,  fixed  carbon,  etc.  So  far  as  the  usual  test  records  are 
concerned,  the  specific  gravity  of  a  bituminous  road  or  paving 
material  is  one  of  the  most  important  characteristics  used  to 
determine  its  identity,  and  this  is  particularly  true  if  its  specific 
gravity  is  considered  in  connection  with  the  consistency  of  the 
material  and  sometimes  its  solubility  in  carbon  disulphide. 
Thus,  a  bituminous  material  with  a  specific  gravity  of  0.99  and 
penetration  of  7.0  millimeters  at  25°  C.  must  be  a  blown  product. 
Fluid  consistency  and  high  specific  gravity,  say  1.25,  in  a  tar 
serves  to  identify  it  as  a  coal  tar,  and  the  identification  is  strength- 
ened if  its  solubility  in  carbon  disulphide  is  low,  say  75  per- 
cent. High  fixed  carbon  in  most  asphalt  cements  produced 
from  Mexican  petroleums  is  a  distinguishing  characteristic.  Rela- 
tively low  fixed  carbon  in  good  asphalt  cements  of  the  same 
consistency  produced  from  California  petroleums,  serve  to  differ- 
entiate them  from  the  Mexican  products.  Here,  again,  the 
necessity  or  desirability  of  different  test  limits  is  apparent,  for 
if  the  amount  of  fixed  carbon  yielded  by  a  California  asphalt 
cement  was  as  high  as  16  percent  often  found  in  Mexican 
asphalt  cements,  indications  would  point  very  strongly  to  injury 
of  the  former,  due  to  excessive  temperatures  having  been  em- 
ployed in  the  process  of  manufacture. 

"This  leads  us  into  the  third  purpose  for  which  tests  may 
be  made  to  serve — control  of  uniformity  in  the  preparation  or 
manufacture  of  a  material.  Among  such  tests  may  be  men- 
tioned those  for  determining  flash  point,  loss  by  volatilization, 
distillation,  solubility  in  given  grades  of  paraffin  naphthas  and 
solubility  in  carbon  tetrachloride.  Practically  all  of  the  other 
tests  previously  enumerated  may  also  be  made  to  serve  this 
end.  No  one  by  itself  will,  however,  necessarily  accomplish 
this  purpose,  no  matter  how  close  the  test  limits  are  drawn. 
This  is  mainly  due  to  the  fact  that  products  of  innumer- 
ably varied  and  complex  characteristics  may  be  produced 


BITUMINOUS   MATERIALS  225 

from  a  given  crude  material  by  modifying  the. methods  of 
manufacture. 

"In  the  preparation  or  interpretation  of  any  specifications 
for  bituminous  road  or  paving  materials,  an  appreciation  of  the 
interrelation  of  tests  and  test  limits  is  as  necessary  as  an  under- 
standing of  the  individual  significance  of  the  tests  themselves, 
and  yet  those  who  should  be  most  familiar  with  such  matters 
often  fail  to  consider  the  possible  relation  which  a  given  test 
may  bear  to  others  with  which  it  is  associated  in  specifications. 
The  interrelation  of  tests  and  test  limits  is  something  which 
the  layman  may  not  readily  comprehend,  and  this  has  often 
resulted  in  his  innocent  acceptance  and  enforcement  of  unjustly 
discriminative  specifications  prepared  or  suggested  by  those  who 
have  an  object  to  attain." 

The  1913  Report*  of  the  Special  Committee  on  "Bituminous 
Materials  for  Road  Construction"  of  the  American  Society  of 
Civil  Engineers  contained  the  following  recommendations  rela- 
tive to  the  advisability  of  using  separate  specifications  for  dif- 
ferent types  of  bituminous  materials  instead  of  using  one  speci- 
fication covering  many  types  of  one  class  of  materials. 

"Your  Committee  has  especially  considered  during  the  past 
year  the  various  methods  of  writing  specifications  covering  the 
physical  and  chemical  properties  of  bituminous  materials  for 
use  in  the  construction  of  bituminous  surfaces  and  bituminous 
pavements.  Many  of  these  properties  vary  to  a  remarkable 
degree,  dependent  primarily  upon  the  source  of  the  material 
and  the  methods  employed  in  refining.  It  is  recognized  that  it 
is  often  essential  to  specify  narrow  limitations  of  certain  proper- 
ties in  order  to  secure  desired  chemical  and  physical  character- 
istics and  uniformity  in  the  manufactured  material.  It  is  not 
in  many  cases  practicable  to  specify  the  same  limitations  except 
for  materials  obtained  from  the  same  or  similar  sources  and 
prepared  in  the  same  manner. 

"Therefore  it  is  suggested  that  for  the  present  at  least,  when- 
ever comprehensive  specifications  are  to  be  prepared  so  as  to 

*  See  February,   1913  Proceedings,  Am.  Soc.  C.  E. 


226  ELEMENTS    OF   HIGHWAY    ENGINEERING 

admit  a  variety  of  types  of  materials,  separate  specifications 
as  may  be  necessary  be  prepared  for  each  type.  As  an  illustra- 
tion, the  specification  for  the  bituminous  cement  to  be  used  in 
the  construction  of  a  bituminous  pavement  by  the  mixing  method 
might  contain  independent  specifications  covering,  within  narrow 
limits,  the  physical  and  chemical  properties  of  each  of  the  fol- 
lowing bituminous  materials :  refined  water-gas  tars,  refined  coal- 
gas  tars,  mixtures  of  tars,  asphalts  containing  native  bitumen 
from  one  or  more  sources,  asphalts  obtained  by  refining  petro- 
leum from  one  or  more  sources,  and  asphalts  which  are  solid 
or  semi-solid  compounds  composed  of  the  bitumens  mentioned 
with  petroleums  or  derivatives  thereof." 


CHAPTER  X 
DUST  PREVENTION  AND  BITUMINOUS  SURFACES 

DUST  PREVENTION 

CLASSIFICATION  OF  SURFACE  TREATMENT  METHODS.  A  pal- 
liative used  as  a  dust  preventive  or  dust  layer  on  the  surface 
of  a  roadway  may  be  defined  as  "material  applied  to  a  roadway 
for  temporarily  preventing  the  formation  or  dispersion  under 
traffic  of  distributable  dust."*  A  bituminous  surface  has  been 
described  as  "a  superficial  coat  of  bituminous  material  with  or 
without  the  addition  of  stone  or  slag  chips,  gravel,  sand,  or 
material  of  similar  character."!  While  it  is  evident  that  the 
reapplication  of  asphaltic  oils,  tars,  and  certain  emulsions  may 
form  bituminous  surfaces,  the  methods  of  construction  considered 
under  this  latter  title  will  be  confined  to  those  treatments  which 
result  in  the  formation  of  bituminous  surfaces  which  are  effica- 
cious under  ordinary  conditions  for  at  least  one  year. 

DEVELOPMENT.  In  1871,  Francou  of  Audi,  France,  spread 
tar  on  the  roadway  surface  and  then  set  fire  to  it  in  order  to 
volatilize  parts  of  the  tar.  In  1896,  Girardeau,  having  noticed 
the  good  results  obtained  when  a  cold  tar  application  was  acted 
upon  by  the  heat  of  the  sun,  applied  hot  tar  to  a  roadway  sur- 
face. It  was  in  1901  that  systematic  experiments  were  carried 
out  by  Dr.  Guglielminetti  at  Monte  Carlo,  Geneva,  and  Nice, 
using  coal  tar  and  brushing  the  same  into  the  road  surface. 
In  Europe,  the  campaign  against  dust  and  the  deterioration  of 
road  surfaces,  caused  primarily  by  motor-car  traffic,  was  thus 
inaugurated  by  Dr.  Guglielminetti.  The  results  of  his  success- 
ful experiments  with  superficial  tarring  at  Monaco  were  pub- 
lished throughout  all  Europe.  In  the  following  year  trials  were 
carried  out  at  Champigny  by  the  engineers  of  the  Department 

*Dec.,  1914  Proceedings,  Am.  Soc.  C.  E.,  page  3014. 
fDec.,  1914  Proceedings,  Am.  Soc.  C.  E.,  page  3012. 
227   ' 


228  ELEMENTS   OF   HIGHWAY  ENGINEERING 

of  Roads  and  Bridges  of  France.  In  the  1903  report  on  these 
trials,  the  French  engineers  formulated  all  the  basic  principles 
of  superficial  tarring. 

It  might  be  said  that  dust  suppression  was  the  main  cause 
of  the  development  of  the  method  of  surface  treatment.  While 
in  Europe  it  led  to  superficial  tarring,  in  this  country  the  first 
trials  of  this  method  were  made  with  light  oils.  Oil  was  used 
for  this  purpose  in  1894  at  Santa  Barbara,  California.  Further 
trials  were  made  in  1898,  and  oils  were  used  to  a  very  slight 
extent  in  different  parts  of  the  country  up  to  1905.  After  1905 
the  use  of  oils  as  a  dust  palliative  rapidly  increased  in  the  United 
States.  Surface  tarring  has  been  used  in  this  country  since  1906. 

FORMATION  OF  DUST.  The  nature  of  the  work  to  be  ac- 
complished in  laying  dust  must  be  understood  before  details 
of  methods  can  be  properly  considered.  In  this  connection  it 
is  necessary  to  know  the  sources  of  the  different  kinds  of  dust 
on  the  surfaces  of  roadways.  A  self-evident  source  of  dust  is 
the  mechanical  abrasion  of  the  road  metal  by  traffic.  It  is 
manifest  that  the  degree  of  abrasion  will  depend  upon  the  amount 
and  nature  of  the  traffic,  the  kind  of  material  used,  and  the 
method  of  construction  and  maintenance  employed.  Other 
sources  of  dust  due  to  traffic  are  the  deposition  of  dirt  which 
has  adhered  to  the  wheels  of  vehicles  coming  from  adjacent 
earth,  gravel,  or  broken  stone  roadways,  from  the  leakage  of 
the  contents  of  loaded  vehicles  both  in  transit  and  while  load- 
ing and  unloading,  and  the  excrements  of  animals.  The  decay 
of  twigs,  bark,  and  leaves,  and  the  deposition  of  pollen,  seeds, 
and  spores  of  various  plants  result  in  the  formation  of  appreci- 
able amounts  of  dust.  Mineral  matter  applied  to  the  surfaces 
of  certain  pavements  to  prevent  slipperiness  is  a  constant  source 
of  dust.  Mills  where  pulverizing  is  carried  on,  textile  estab- 
lishments, and  foundries  are  prolific  sources  of  dust,  while  soot 
and  fine  ashes  from  chimneys  find  their  way  to  the  streets. 
From  the  nature  of  these  sources  it  is  apparent  that  the  com- 
position of  street  dust  is  complex. 

EFFECTS  OF  DUST.  The  ways  in  which  dust  acts  as  an 
enemy  to  the  public  welfare  may  be  summarized  as  follows: 


DUST  PREVENTION  229 

first,  the  formation  of  heavy  dust  clouds  by  traffic  to  such  an 
extent  as  to  obscure  a  view  of  the  roadway;  second,  when  wet, 
the  formation  of  mud  which  may  cause  skidding  of  wheels  and 
dangerous  footing  for  both  man  and  beast;  third,  the  lowering 
in  real  estate  values  where  it  occurs  in  large  quantities;  fourth, 
the  soiling  of  clothing  and  other  personal  property;  fifth,  its 
action  as  an  abrasive  agent  upon  certain  surfaces;  sixth,  its 
harmful  effect  on  plant  life;  and  seventh,  as  a  distributor  of 
disease  germs. 

The  Pathogenic  Effects  of  Dust  have  been  given  extensive 
study  by  the  medical  profession.  From  what  has  been  said 
relative  to  the  sources  of  dust,  it  is  obvious  that  it  is  made 
up  of  organic  and  inorganic  matter.  If  germ  cultures  are  pre- 
pared from  air,  bacterial  life  of  different  kinds  will  be  found 
present  in  quantities  which  are  sometimes  startling.  Although 
it  is  very  commonly  believed  that  dust  is  full  of  tuberculosis 
germs,  many  bacteriologists  are  not,  positive  on  this  point.  Dr. 
T.  Mitchell  Prudden  states  that  "It  is  certain  that  in  the  country 
and  also  in  cities  whose  streets  are  kept  decently  clean,  there 
is  less  danger  of  harm  from  the  inhalation  of  germs  of  con- 
sumption or  of  any  other  disease,  because  the  constant  purifying 
agency  of  wind  and  air  currents  will  either  soon  sweep  away 
the  dust  or  so  largely  dilute  it  that  it  will  be  practically  free 
from  disease  germs,  the  sources  of  which  are  so  comparatively 
limited.  If,  however,  the  streets  of  cities  be  or  are  allowed  to 
remain  filthy,  so  that  abundant  and  pretty  constant  clouds  are 
encountered  by  those  passing  through  them;  if  the  streets  are 
not  properly  sprinkled  before  sweeping,  either  by  machine  or 
hand;  if  ignorant  or  careless  street  cleaners  are  allowed  to 
scatter  clouds  of  dust  about  them  as  they  sweep  or  shovel  or 
transport  the  pulverized  filth,  the  chances  of  inhalation  of  dan- 
gerous dust  particles  are  proportionately  increased.  But  on  the 
whole,  the  risk  of  infection  out  of  doors  from  dust,  even  in 
crowded  towns,  unless  they  are  notably  filthy,  is  not  actually 
very  great."  Dust,  however,  may  aid  in  the  contraction  of 
tuberculosis  even  though  it  contains  no  tubercle  bacilli.  The 
constant  inhalation  of  dust  will  irritate  the  pulmonary  organs 


230  ELEMENTS   OF   HIGHWAY   ENGINEERING 

so  as  to  render  them  more  susceptible  to  the  attack  of  the  tubercle 
bacilli,  which  are  frequently  lodged  in  the  mucous  membranes 
of  healthy  individuals.  Various  delicate  membranes  are  irritated 
by  the  simple  mechanical  action  of  the  dust.  The  membranes 
of  the  respiratory  organs  are  susceptible  to  this  influence,  espe- 
cially if  a  person  be  asthmatic.  The  membranes  of  the  eye 
are  also  frequently  seriously  irritated  by  dust.  In  foreign  coun- 
tries where  the  dust  problem  has  been  successfully  solved,  physi- 
cians report  a  marked  falling  off  in  the  number  of  cases  of 
conjunctivitis. 

USE  OF  PALLIATIVES.  European  engineers  appreciate  the 
true  value  of  palliatives,  as  both  at  the  First  International  Road 
Congress  held  in  Paris  in  1908  and  at  the  Second  Congress 
held  in  Brussels  in  1910,  conclusions  were  adopted  to  the  effect 
"that  emulsions  of  tars  or  oils,  hygroscopic  salts,  etc.,  are  really 
efficient,  but,  unfortunately,  only  for  a  short  time.  Therefore 
their  use  should  be  limited  to  special  cases,  such  as  race  courses, 
festivals,  processions,  etc."  Palliatives  are  used  efficiently  in 
America  on  earth,  sand-clay,  gravel,  and  broken  stone  road- 
ways of  certain  classes  of  highways.  Many  consider  that  palli- 
atives should  be  used  only  in  connection  with  earth,  sand-clay, 
and  gravel  roadways,  broken  stone  roadways  subjected  to  light 
horse-drawn  vehicles  and  a  few  motor  vehicles  per  day,  and  for 
broken  stone  roadways  in  poor  repair.  The  prevention  of 
dust  on  bituminous,  cement-concrete,  brick,  wood  block,  and 
stone  block  pavements  should  not  be  accomplished  by 
using  palliatives.  The  use  of  palliatives  on  pavements  is 
wrong  in  principle.  Sanitary  conditions  require  the  constant 
removal  of  filth  from  roadways,  and  if  this  is  removed  periodi- 
cally by  flushing  or  other  means,  the  effectiveness  of  dust-laying 
processes  is  curtailed.  Furthermore,  the  fine  dust  which  neces- 
sitates the  use  of  palliatives  should  be  removed.  Dust  preven- 
tion on  pavements  is  primarily  a  problem  in  street  cleaning  and 
will  be  considered  in  detail  in  the  chapter  covering  that  subject. 

It  is  evident  that  the  field  of  usefulness  of  palliatives  is 
limited.  This  field  will  grow  comparatively  smaller  in  the 
future  as  the  mileage  of  good  roads  and  pavements,  increases, 


DUST  PREVENTION  231 

as  the  economics  of  construction  and  maintenance  is  under- 
stood, and  as  the  inherent  value  of  the  various  methods  for  the 
elimination  of  dust  is  recognized. 

In  Europe  attention  to  aesthetics  has  resulted  in  the  use  of 
palliatives  where  otherwise  bituminous  surfaces  would  have  been 
employed.  At  the  birthplace  of  the  campaign  against  dust  by 
the  use  of  superficial  tarring,  namely,  in  the  Principality  of 
Monaco,  ordinary  watering  is  used  to  lay  the  dust  on  the  boule- 
vards surrounding  the  beautiful  gardens  in  front  of  the  Monte 
Carlo  Casino.  The  watering  of  these  surfaces  once  per  hour 
serves  to  lay  the  dust,  cool  the  atmosphere,  and  furnish  a  road- 
way surface  which  is  in  harmony  with  its  magnificent 
environments. 

CLASSIFICATION  OF  PALLIATIVES.  Palliatives,  which  are  in 
common  use  as  dust  preventives,  include  water,  sea-water,  salt 
solutions,  calcium  chloride,  tar  and  oil  emulsions,  and  light  oils 
and  tars.  As  oils  and  tars  are  included  in  this  classification, 
the  distinction  between  treatments  with  palliatives  and  the 
construction  of  bituminous  surfaces  should  be  borne  in  mind. 

Water.  Water  is  an  effective  dust  layer  when  properly  ap- 
plied under  the  direction  of  engineers  who  supervise  the  details 
of  the  method  of  application.  Due  to  the  brief  period  of  effi- 
ciency of  one  application,  the  use  of  water  as  a  dust  layer  is 
limited  from  an  economical  standpoint.  Furthermore,  it  has 
been  demonstrated  by  many  service  tests  that  watering,  even 
when  properly  accomplished,  will  not  preserve  broken  stone  or 
gravel  roads  when  the  traffic  consists  of  rapidly  moving  motor- 
cars. Based  on  the  above  conclusion,  it  is  seen  that  watering 
of  highways  outside  urban  districts  is  generally  impracticable 
since  the  cost  of  watering  where  waterworks  systems  do  not 
exist,  is  prohibitive  on  account  of  the  long  hauls  from  the  source 
of  water  supply,  and  as  there  are  few  communities  where  regula- 
tions covering  the  maximum  rate  of  speed  are  enforced  except 
in  built-up  districts. 

Watering  for  the  purpose  of  dust  laying  is  not  regarded 
favorably  in  many  municipalities  because  this  class  of  work, 
being  in  the  hands  of  inexperienced  and  untrained  laymen,  is 


232  ELEMENTS   OF  HIGHWAY   ENGINEERING 

done  in  an  inefficient  and  costly  manner.  Generally  the  details 
of  watering  are  left  to  ignorant  and  irresponsible  drivers  of 
watering-carts.  Under  these  conditions  it  is  not  surprising  that 
watering  means  muddy  streets  to  most  citizens. 

There  is  an  efficient  and  economical  manner  of  accomplishing 
every  method  of  construction  and  maintenance  of  highways. 
Watering  is  no  exception  to  the  rule.  The  broken  stone  or 
gravel  roadway  should  be  kept  repaired  so  that  its  surface  is 
free  from  pot-holes,  ruts  and  other  depressions.  Surplus  dust 
must  be  removed  before  the  water  is  applied.  Watering-carts 
must  be  used  with  which  water  may  be  distributed  uniformly 
and  in  small  amounts  per  square  yard  of  roadway.  Pressure 
distributors,  similar  in  design  to  machines  used  for  the  appli- 
cation of  light  tars  and  oils,  may  be  economically  employed 
for  this  purpose.  Instead  of  flooding  the  surface,  it  should  only 
be  dampened.  Dependent  upon  climatic  conditions  and  local 
peculiarities  of  a  given  street,  such  as  the  character  of  the  road- 
way surface,  shade  trees,  buildings,  etc.,  from  one  to  eight  ap- 
plications per  day  will  be  required  to  lay  the  dust  and  keep 
the  street  from  being  objectionably  dusty.  The  annual  cost 
of  watering  in  the  manner  described  from  May  to  October  will 
range  from  2  to  $%  cents  per  square  yard. 

Sea- Water.  The  use  of  salt  water  has  not  been  developed 
sufficiently  to  establish  its  value  and  rating  as  a  dust  palliative. 
It  has  been  tried  in  a  number  of  instances  in  coast  towns  and 
cities,  usually  being  applied  with  the  ordinary  watering-cart. 
In  one  instance  it  was  found  that  in  dry  weather  it  formed  a 
hard,  salty  scale,  while  in  wet  wreather  the  mud  contained  so 
much  salt  that  it  injured  the  iron  and  varnish  of  vehicles.  In 
another  case  it  was  found  that  sea-water  was  about  three  times 
as  effective  as  fresh  water  in  preventing  dust  and,  when  prop- 
erly applied,  had  no  injurious  effects  on  the  surface  of  the 
roadway. 

Calcium  Chloride.  This  material  is  a  by-product  in  the 
ammonia-soda  process  of  manufacturing  common  washing  soda 
and  in  other  industrial  processes.  It  is  shipped  in  granulated 
form  in  air-tight  steel  drums.  Calcium  chloride  is  used  in  two 


DUST   PREVENTION  233 

ways  in  connection  with  dust  laying:  first,  by  the  "wet"  method 
and,  second,  by  the  "dry"  method.  When  applied  dry  to  the 
cleaned  road  surface,  see  Fig.  76,  a  distributing  apparatus,  such 
as  a  lime  spreader,  should  be  employed.  From  K  to  il/4  pounds 
per  square  yard  are  used  for  one  application.  Usually  two  ap- 
plications per  season  in  the  North  will  give  good  results.  The 


FIG.  76.     Application  of  Calcium  Chloride  by  the  "Dry"  Method. 

cost  per  season  varies  from  1.75  to  4  cents  per  square  yard. 
When  applied  wet,  the  calcium  chloride  is  dissolved  at  the  rate 
of  i  pound  to  i  gallon  of  water,  using  about  one-third  gallon 
of  solution  per  square  yard.  For  the  application  of  the  solu- 
tion ordinary  watering-carts  are  generally  used,  although  with 
pressure  distributors  it  is  practicable  to  secure  more  uniform 
distribution.  The  usual  method  is  to  use  two  applications  along 
the  center  of  the  street  and  one  at  the  sides.  To  secure  freedom 
from  dust  about  ten  applications  should  be  used  per  season 
in  Northern  States. 

The  most  scientific  work  which  has  been  done  with  calcium 
chloride  was  that  carried  on  by  a  Committee  of  Judges  of  the 
Roads  Improvement  Association  of  England  in  1909  and  1910. 
After  exhaustive  experiments  the  following  conclusions  were  de- 


234  ELEMENTS   OF   HIGHWAY   ENGINEERING 

duced:  "We  are  of  opinion  that  the  results  of  the  tests  of  calcium 
chloride  applied  in  granular  form  by  the  'dry'  method  have  shown 
that  it  is  a  very  effective  dust  layer;  that  the  treatment  has  the  ill 
effects  of  causing,  during  the  winter  months,  an  abnormal  quan- 
tity of  sticky  mud,  a  decided  tendency  to  licking  up,  and  a 
disintegrating  action  upon  the  macadam  surface." 

Emulsions.     Palliatives  belonging  to  this  class  are  mixtures 
of  oil,  water  and  a  saponifying  agent.     The  saponifying  agent 


FIG.  77.     Pressure  Distributor  Used  for  Applying  Light  Oils. 

forms  a  chemical  solution  with  the  water.  The  mixture  is  readily 
nu'scible  with  the  oil.  Alkalies  such  as  potash,  soda,  ammonia, 
and  various  soap  solutions  are  the  agents  most  commonly  used 
with  oils.  A  concentrated  emulsion  might  consist  of  5  percent 
soap,  30  percent  water  and  65  percent  oil.  Twenty  percent  of 
this  emulsion  with  80  percent  water  might  be  used  for  the  first 
application  and  a  5  to  10  percent  solution  for  retreatments. 
Oil  emulsions  are  commonly  used  although  tar  emulsions  are 
employed  to  a  small  extent  in  this  country.  Distribution  is 
usually  made  with  an  ordinary  watering-cart  on  the  unprepared 
surface,  although  better  results  may  be  obtained  by  cleaning 
the  roadway  surface  and  using  some  type  of  pressure  distributor. 
Sometimes  a  light  sand  coat  has  be£n  added,  but  as  a  rule  the 


DUST  PREVENTION 


235 


surface  is  left  uncovered.  From  six  to  ten  treatments  are  used 
in  a  season,  extending  from  April  to  October.  The  cost  varies 
from  1.5  to  3  cents  per  square  yard  for  the  season. 

Light  Oils  and  Light  Tars.  In  this  group  of  palliatives  may 
be  included  crude  and  refined  petroleums,  water-gas  tars,  coal- 
gas  tars,  and  certain  proprietary  compounds.  Light  oils  were 
employed  in  1898  in  Los  Angeles  and  Algeris  for  the  purpose 
of  laying  dust.  Their  use  has  developed  rapidly  in  America 


FIG.  78.     Surface  of  Roadway  Showing  Uniform  Application  of  Light  Oil. 

due  to  the  large  supply  available,  while  in  Europe  very  little 
oil  has  been  used  as  the  price  of  oil  is  comparatively  high.  The 
tendency  in  Europe  has  been  to  discard  all  types  of  palliatives 
and  to  employ  in  their  place  bituminous  surfaces  which  will  be 
efficacious  for  at  least  a  year. 

Light  oils  and  light  tars  having  proper  physical  and  chemical 
properties  are  efficient  dust  layers.  They  should  be  used  in 
small  amounts  as  palliatives,  otherwise  a  soft  greasy  surface 
will  result.  The  material  is  usually*  applied  cold,  using  ordi- 
nary sprinkler  carts  or  distributors,  of  either  the  gravity  or 
pressure  type.  In  order  that  this  class  of  palliatives  should  be 
distributed  economically  and  satisfactorily,  pressure  distributors 
should  be  used  which  are  equipped  with  suitable  hoods  to  pro- 


236  ELEMENTS   OF  HIGHWAY   ENGINEERING 

tect  pedestrians  and  property  from  the  fine  spray  accompanying 
distribution,  and  which  are  capable  of  distributing  the  material 
in  as  small  amounts  as  y&  of  a  gallon  per  square  yard.  The 
accompanying  photographs,  see  Figs.  77  and  78,  show  respec- 
tively a  distributor  of  the  type  described  and  an  efficient  appli- 
cation of  a  light  oil.  There  would  be  few  complaints  of  ruination 
of  clothes  and  house  furnishings,  filthy  streets,  and  disagree- 
able odors  if  this  method  of  distribution  was  universally 
employed. 

Light  oils  and  light  tars  are  effective  for  six  weeks  to 
two  months  if  properly  applied.  The  amount  used  per  square 
yard  should  be  between  %  and  y&  of  a  gallon,  dependent  on 
the  kind  of  material  and  the  condition  of  the  surface  of  the 
roadway.  If  more  than  this  amount  is  used,  the  oil  may  work 
down  into  the  wearing  course  and,  serving  as  a  lubricant,  cause 
disintegration  by  the  formation  of  a  loose  surface.  They  should 
not  be  employed  after  November  i  in  the  Northern  States  as 
a  muddy,  greasy  surface  would  probably  form  on  the  roadway 
during  a  part  of  the  winter.  It  has  been  claimed  that  by  the 
use  of  light  oils,  broken  stone  water-bound  roadways  could  be 
preserved  under  high-speed  motor-car  traffic.  This  fallacy  has 
caused  a  large  waste  of  public  funds  in  many  cases,  since  the 
broken  stone  roadway  has  begun  to  disintegrate  within  two  to 
three  weeks  after  the  application  of  the  oil,  although  the  effec- 
tiveness of  the  application  as  a  dust  layer  was  apparent  for  six 
weeks. 

In  1909  over  75  miles  of  the  state  highways  of  Rhode  Island 
were  oiled.  The  quantity  of  oil  used  per  square  yard  was  0.2 
gallon,  and  the  average  cost  per  application  was  about  0.9 
cents  per  square  yard.  In  Philadelphia,  during  1914,  the  cost 
per  treatment  of  0.2  gallon  per  square  yard  averaged  1.13 
cents. 

Although  there  are  many  proprietary  palliatives  on  the 
market,  they  will  not  be  considered,  first,  because  they  appear 
to  be  of  more  or  less  transitory  character,  and,  second,  because 
the  fundamental  principles  underlying  the  use  of  palliatives  have 
been  explained. 


BITUMINOUS  SURFACES  237 

BITUMINOUS  SURFACES 

Bituminous  surfaces  are  used  on  broken  stone  and  gravel 
roads,  on  bituminous  and  cement-concrete  pavements,  and  to 
a  certain  extent  on  brick  and  wood  block  pavements.  In  this 
chapter  will  be  considered  methods  of  constructing  and  main- 
taining bituminous  surfaces  on  broken  stone  and  gravel  roads, 
while  bituminous  surfaces  on  bituminous  macadam  pavements, 
bituminous  concrete  pavements,  asphalt  block  pavements,  ce- 
ment-concrete pavements,  brick  and  wood  block  pavements  will 
be  treated  in  the  chapters  devoted  to  the  several  pavements. 

BITUMINOUS  MATERIALS.  The  different  kinds  of  bituminous 
materials  used  are  asphaltic  oils,  asphalts,  crude  and  refined 
water-gas  tars,  crude  and  refined  coal-gas  tars,  combinations  of 
refined  tars,  and  combinations  of  refined  tars  and  asphalts. 

There  has  been  noted  a  growing  objection  to  the  use  of 
materials,  for  the  construction  of  bituminous  surfaces,  which 
require  from  two  to  six  weeks  to  set  up  to  such  an  extent  that 
tracking  will  not  occur.  Materials,  which  have  given  satis- 
factory results  from  this  standpoint,  are  refined  coal  tars  and 
water-gas  tars,  asphalts,  combinations  of  asphaltic  materials 
and  refined  tars,  and  cut-back  asphaltic  oils.  Within  24  to  48 
hours,  bituminous  surfaces  constructed  with  the  foregoing  ma- 
terials, using  from  ^  to  ^  gallon  per  square  yard  and  a  thin 
covering  of  stone  chips,  have  set  up  so  that  no  tracking  is 
noticeable. 

CONSTRUCTION.  Preparation  of  Road  Surface.  Before  con- 
structing a  bituminous  surface  on  a  broken  stone  or  gravel 
road,  all  depressions,  pot-holes,  ruts,  or  other  irregulari- 
ties should  be  filled  with  thoroughly  compacted  bitumi- 
nous-coated stone  so  that  the  whole  surface  of  the  road- 
way is  even.  All  surplus  dust  must  be  removed  so 
that  the  larger  pieces  of  broken  stone  of  the  roadway 
surface  are  exposed  but  without  breaking  the  bond.  This 
cleaning  process  is  accomplished  by  the  use  of  horse  sweepers 
and  fine  bass  brooms,  with  coarse  fibre  brooms  and  fine  bass 
brooms,  see  Fig.  79,  or  by  a  vacuum  process.  If  there  is  caked 


238 


ELEMENTS   OF   HIGHWAY  ENGINEERING 


mud  on  the  surface  of  the  roadway,  wet  brushing  will  prove 
advantageous.  It  is  apparent  that  the  character  of  the  cleaned 
surface  will  be  affected  by  the  method  which  was  used  in  the 


FIG.  79.     Coarse  Fibre  Broom  (left)  and  Bass  Fibre  Broom  (right). 


FIG.  80.     Surface  of  Macadam  Road  Showing  Large  Broken  Stone. 

original  construction  of  the  roadway.  If  the  practice  of  French 
engineers  in  using  large-size  stone  varying  from  an  inch  to  2^ 
inches  in  longest  dimensions  for  the  top  course  of  a  broken 
stone  road  is  followed,  and  the  stone  is  hard  and  tough,  the 
desired  surface,  see  Fig.  80,  can  be  easily  secured.  The  large 


BITUMINOUS   SURFACES  239 

stones  in  such  a  roadway  are  exposed  and  the  layer  of  dust, 
so  characteristic  of  broken  stone  surfaces  composed  of  small 
stone,  has  thus  been  practically  eliminated.  A  clean  mosaic 
surface  is  of  the  utmost  importance  from  the  standpoint  of  the 
formation  of  a  satisfactory  bond  between  the  broken  stone  and 
the  bituminous  material.  The  maintenance  of  bituminous  sur- 
faces on  wearing  courses  of  large  broken  stone  is  economical, 
since  after  the  bituminous  surface  wears  away  in  spots,  the 
mechanically  interlocked  large  stones  will  of  themselves  gener- 
ally have  sufficient  stability  to  withstand  the  effects  of  traffic 
until  retreated.  On  the  other  hand,  if  the  top  course  of  a  broken 
stone  road  has  been  constructed  of  a  product  of  the  crusher, 
varying  in  size  from  %  to  \1/^  inch  material,  it  will  be  very 
difficult  to  secure  a  clean  surface..  When  the  bituminous  ma- 
terial is  applied  the  roadway  surface  should  be  bone  dry.  If 
the  surface  is  damp  it  will  be  difficult  to  secure  a  good  bond. 

Application  of  Bituminous  Material.  Distribution  of  the 
bituminous  material  is  accomplished  by  two  methods.  Flow  by 
gravity  is  utilized  in  one  method  and  mechanical  pressure  in 
the  other.  The  use  of  gravity  distributors  has  not  been  de- 
veloped to  its  fullest  extent  in  America,  in  that  the  use  of  me- 
chanical brushes  or  the  brushing  of  the  material  into  the  road 
by  hand  brooming  has  never  been  adopted  extensively.  The 
advantages  claimed  for  pressure  distributors  are:  aid  in  clean- 
ing the  surface  of  the  roadway,  even  application,  distribution 
of  small  amounts  per  square  yard,  and  satisfactory  adhesion 
obtained  between  the  bituminous  material  and  the  surface  of 
the  roadway.  By  brushing  after  gravity  distribution,  it  is  pos- 
sible to  distribute  uniformly  %  to  */s  of  a  gallon  per  square 
yard  of  many  of  the  bituminous  materials  used  for  the  con- 
struction of  bituminous  surfaces.  In  some  cases,  when  the  dis- 
tribution is  accomplished  by  hand  brooming,  the  adhesion  of 
the  material  to  the  road  metal  is  as  good  as  when  the  material 
is  applied  under  pressure. 

Amount  of  Bituminous  Material.  As  a  general  rule  from 
%  to  y%  gallon  per  square  yard  is  used  for  the  first  treatment. 
In  some  cases,  however,  as  small  an  amount  as  ^  of  a  gallon 


240 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


per  square  yard  is  employed.  The  amount  applied  per  treat- 
ment depends  upon  the  kind  of  bituminous  material,  the  char- 
acter and  condition  of  the  surface,  and  the  details  of  the  method 
of  application. 

Top  Dressing.     The  superficial  coat  of  bituminous  material 
is  usually  covered  with  either  coarse  sand,  fine  gravel,  or  stone 


FIG.  81.      Warren  Brothers  Hand-drawn  Sand  or  Stone-Chip  Distributor. 

chips  varying  from  y&  of  an  inch  to  ^  an  inch  in  longest  dimen- 
sions. The  amount  of  sand,  stone  chips,  or  gravel  used  per 
square  yard  depends  upon  the  quantity  and  kind  of  the  bitum- 
inous material.  From  7  to  15  pounds  per  square  yard  have 
been  used  satisfactorily.  Top  dressing  is  distributed  by  hand 
and  machine  methods.  In  the  machines,  see  Fig.  8 1 ,  employed 
for  this  purpose,  the  mineral  matter  falls  on  a  revolving  cone 
beneath  the  body  of  the  wagon  and  is  thus  uniformly  spread  over 
the  surface. 

COST  DATA.  The  cost  of  constructing  a  bituminous  surface 
varies  from  4  to  10  cents  per  square  yard. 

MAINTENANCE.  The  life  of  a  bituminous  surface  and  its 
economical  use  depend  primarily  upon  traffic  conditions,  the 
method  of  construction,  and  the  nature  of  the  bituminous  mate- 


BITUMINOUS   SURFACES  241 

rial  used.  With  the  heavier  grades  of  bituminous  materials 
adaptable  for  this  work,  if  the  road  is  subjected  to  a  normal 
traffic  for  which  the  method  and  material  are  economical  and 
suitable,  retreatment  is  necessary  every  one  or  two  years.  Under 
traffic  conditions  demanding  some  other  type  of  construction, 
it  may  be  necessary  to  retreat  the  road  twice  each  year,  as  is 
done  in  the  case  of  the  Avenue  du  Bois  de  Boulogne  in  Paris. 
Retreatments  can  generally  be  accomplished  by  using  a  smaller 
amount  of  bituminous  material,  usually  about  half  the  amount 
used  in  the  first  treatment.  The  same  care  should  be  taken 
in  preparing  the  road  surface  as  is  done  in  the  original  treat- 
ment. Continuous  repairing  methods  are,  of  course,  productive 
of  the  most  satisfactory  results.  As  it  is  difficult  to  barricade 
a  road  after  small  repairs  have  been  made,  a  method  should 
be  used  which  will  prevent  displacement  of  the  road  metal 
employed  in  patching. 

MECHANICAL  APPLIANCES.  The  appliances  used  in  the  dis- 
tribution of  bituminous  materials  may  be  classified  as  gravity 
distributors  and  pressure  distributors.  As  the  demand  developed 
for  a  heavier  binder,  both  for  surface  treatment  and  penetration 
work,  machines  especially  designed  for  distributing  these  ma- 
terials began  to  appear.  The  market  is  supplied  with  so  many 
different  types,  each  one  of  which  is  claimed  to  be  "the  dis- 
tributor," that  a  thorough  investigation  is  essential  preceding 
the  purchase  of  machines  for  various  classes  of  work. 

Gravity  Distributors.  In  this  subdivision  will  be  considered 
pouring  cans,  tanks  with  hose  attached,  and  distributing  machines. 

Pouring  Cans.  With  the  use  of  pouring  cans  alone  it  is 
difficult  to  secure  uniform  application  of  the  bituminous 
material.  If  the  application  of  the  material  is  immediately 
followed  by  vigorous  brushing  with  fibre  push  brooms,  very  sat- 
isfactory surfaces  can  be  obtained.  The  use  of  these  methods 
will  result  in  a  high  labor  cost  due  to  two  factors,  the  high  cost 
of  labor,  especially  in  the  United  States,  and  the  slow  progress 
made.  Cans  should  be  used  with  which  may  be  secured  the 
maximum  uniformity  of  application  attainable  by  this  method 
of  distribution.  (See  Fig.  82.) 


242 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


Hand-Drawti  Gravity  Distributors.     The  advantages  of  hand- 
drawn  distributors  over  pouring  cans   are   the   more  uniform 


FIG.   82.     "Perfection"   Pouring  Can   with   which   Bituminous   Material   is 
Distributed  in  a  Sheet. 


FlG.  83.     "Eldus"  Hand-drawn  Distributor.     (American  Machine.) 

distribution  of  material,  the  elimination,  to  a  certain  extent,  of 
the  personal  equation,  more  rapid  work,  and  the  practicability 


BITUMINOUS    SURFACES 


243 


of  keeping  the  bituminous  material  at  a  higher  and  more  even 
temperature.  (See  Fig.  83.)  A  hand-drawn  gravity  distributor, 
as  shown  in  Fig.  84,  was  introduced  in  France  in  1903. 

Tanks  with  Hose  Attached.     If  a  tank  from  which  the  bitu- 
minous material  flows  by  gravity  through  a  hose  and  nozzle 


Courtesy  of  Dr.  Guglielminetti. 

FIG.  84.     French  Hand-drawn  Distributor. 

onto  the  road  is  used,  brushing  is  necessary    to    secure    satis- 
factory distribution. 

Machines  with  Distributing  Apparatus.  Watering  carts  were 
first  used  in  the  United  States  for  distributing  the  light  oils 
and  tars  for  suppressing  the  dust.  The  ordinary  spray  attach- 
ments on  the  carts  were  not  very  satisfactory  for  distributing 
this  class  of  material.  Attention  was  then  directed  to  modify- 
ing the  distributing  device,  still  using  the  wooden-tank  wagon. 
Practically  all  of  the  modifications  consisted  in  substituting  for 
water  sprinklers  one  or  more  horizontal  pipes  pierced  with  small 
holes.  These  pipes  were  attached  to  the  outlet  pipe  of  the  tank 
and  were  placed  parallel  to  the  back  axle  at  the  rear  of  the  tank. 
The  pipes  were  usually  about  the  same  length  as  the  gauge  of 
the  rear  wheels.  The  material  flowed  through  these  pipes  in 


244 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


small  vertical  streams  onto  the  road  surface.  Hence,  in  dis- 
tributing small  quantities,  the  road  surface  would  not  be  entirely 
covered  with  the  material.  Traffic  worked  the  material  around 
on  the  road  surface  so  that  in  the  course  of  time  a  fairly  satis- 
factory result  might  be  obtained.  In  some  American  machines, 


FIG.  85.     The  A.  T.  C.  Gravity  Distnoutor. 

see  Fig.  85,  the  material  flows  from  pipes  onto  a  flash  board 
and  from  the  board  to  the  surface  of  the  roadway  in  the  form 
of  a  sheet. 

The  general  practice  in  Europe  in  using  machines  of  this 
type  is  to  follow  the  distribution  by  brushing  the  material  into 
the  road.  This  is  done  either  by  hand  brooming  or  by  brooms 
which  are  attached  directly  behind  the  distributor.  The  brooms 
are  either  of  the  drag  or  rotary  type.  The  machines  are  made 
to  be  drawn  by  hand  or  by  horse.  (See  Fig.  86.) 

Pressure  Distributors.  The  various  types  of  distributing 
machines  of  this  class  may  be  grouped  in  the  following  sub- 
divisions: hand-drawn  distributors;  pressure  tanks  to  which  are 


BITUMINOUS    SURFACES 


245 


attached  hose  and  spraying  devices  or  horizontal  distributing 
apparatus;  and  machines  equipped  with  mechanical  power- 
pumps  between  the  tank  and  the  distributing  apparatus. 


FIG.  86.     Lassailly  Gravity  Distributor.     (French  Machine.) 


FIG.  87.     English  Hand-drawn  Pressure  Distributor. 

Hand-Drawn  Pressure  Distributors.  In  the  European  ma- 
chines, an  example  of  which  is  shown  in  Fig.  87,  the  material 
is  pumped  from  the  tank  through  a  length  of  flexible  hose  to 


246  ELEMENTS    OF   HIGHWAY   ENGINEERING 

the  outlet  end  of  which  is  fixed  an  iron  pipe  fitted  with  one  or 
more  nozzles.  The  nozzle  is  of  such  a  form  that  the  material 
is  thrown  in  a  fine  cone-shaped  spray.  In  one  type  of  American 
machine,  shown  in  Fig.  88,  the  heated  material  is  pumped  into 
the  distributor  and  applied  to  the  roadway  surface  by  pressure 
from  a  tank  of  compressed  air. 


^ 

FIG.  88.  "Cyclone"  Pressure  Distributor. 

Pressure  Tanks.  These  machines  consist  of  steel  tank  wagons 
equipped  with  steam  coils  and  with  either  a  flexible  hose  with  a 
nozzle  attached  or  a  system  of  pipes  equipped  with  nozzles. 
The  tanks  are  hauled  by  a  steam  roller  which  supplies  steam 
for 'heating  the  material  in  the  tank  and  furnishes  the  steam 
for  the  pressure.  The  bituminous  material  is  forced  out  by  the 
pressure  of  the  steam  between  the  material  and  the  top  of  the 
tank.  (See  Fig.  89.) 

Pressure  Distributors  Equipped  with  Mechanical  Power  Pumps. 
Several  pressure  machines  of  this  type  have  been  invented  in 
the  United  States.  The  distributing  devices  of  all  of  these  ma- 
chines are  alike  in  having  horizontal  pipes  fitted  with  nozzles. 
The  machines  differ  somewhat  in  the  way  the  pressure  is  ob- 
tained and  applied.  Pumps,  run  by  a  sprocket-drive  attach- 
ment on  the  rear  axle,  see  Fig.  90,  by  steam  and  by  gasoline, 


BITUMINOUS    SURFACES 


247 


are  utilized.     Horses  and  steam-rollers  are  used. for    hauling. 
Some  distributors  are  mounted  on  motor  trucks.  (See  Fig.  91.) 


FIG.  80.     Pillsbury  Pressure  Distributor.     (American  Machine.) 


FlG.  90.     Hedeline  and  Voisembert  Pressure  Distributor.     (French  Machine.) 

CHARACTERISTICS.  Advantages.  A  properly  constructed 
bituminous  surface  on  a  broken  stone  or  gravel  road  is  imper- 
vious and  is  easily  cleaned.  It  increases  the  durability  of  the 
road,  yields  no  dust  due  to  abrasion  of  the  roadway  surface, 


w 


BITUMINOUS    SURFACES  249 

and  enables  the  crown  to  be  reduced.  The  ease  of  traction 
and  the  character  of  foothold  will  depend  upon  the  kind  and 
amount  of  the  bituminous  material  used  and  the  grade  of  the 
road.  When  asphaltic  materials  are  used  the  noise  caused  by 
horse-drawn  vehicles  is  comparable  to  that  characteristic  of 
wood-block  pavements  subjected  to  the  same  kind  of  traffic, 
while  bituminous  surfaces  constructed  with  a  thin  coat  of  tar 
give  forth  much  more  noise,  in  some  cases  comparable  to  that 
emanating  from  the  impact  of  horse-drawn  vehicle  traffic  on 
sheet  asphalt  pavements.  It  is  self-evident  that  the  various 
types  of  bituminous  surfaces  are  adaptable  to  many  conditions, 
hence  complete  preliminary  investigations  are  requisite  before 
the  kind  of  material  and  the  details  of  the  method  of  con- 
struction are  adopted. 

Disadvantages  of  Tar  Surfaces.  Slipperiness.  Some  ob- 
jection has  been  raised  in  England  to  superficially  tar-coated 
roads,  due  to  alleged  slipperiness.  Without  doubt  much  slipperi- 
ness  is  due  to  a  smooth  coat  of  tar,  the  ideal  mosaic  surface 
of  tar  and  stones  not  being  secured.  Heavy  traffic  and  late 
tarring  contribute  to  greasiness  of  a  road  with  consequent  slip- 
periness, since  tar  applied  late  in  the  year  and  subjected  to 
heavy  traffic  works  up  into  an  emulsion  more  readily  than  tar 
which  was  applied  at  the  beginning  of  the  season  and  has 
set  hard  by  winter. 

Danger  to  Fish  Life.  There  is  no  danger  of  pollution  of  fish 
streams  if  proper  precautions  are  taken  during  the  treatment 
of  a  road  and  if  refined  tar  is  employed.  It  has  been  shown  that 
if  crude  tars,  having  considerable  ammoniacal  liquor,  are  used  in 
a  manner  which  will  permit  of  portions  of  the  tar  being  washed 
into  the  stream,  it  will  result  in  killing  certain  kinds  of  fish, 
trout  being  especially  susceptible. 

Injury  to  Vegetation.  The  opinion  has  been  expressed  by 
many  that  superficial  tarring  does  not  injure  vegetation  except 
from  the  possible  prevention  of  the  percolation  of  water  through 
the  road  surface  to  the  roots  of  trees.  Although  certain  horti- 
culturists in  France  have  claimed  that  tarred  dust  injures  vege- 
tation, proof  of  this  assertion  has  not  as  yet  been  presented. 


250  ELEMENTS   OF   HIGHWAY   ENGINEERING 

Disadvantages  of  Asphaltic  Oils.  Among  the  disadvantages 
of  using  asphaltic  oil  of  certain  types  may  be  mentioned  the 
ruining  of  carriage  varnish,  clothing,  and  floor  coverings  by  the 
black  greasy  mud  which  is  characteristic  of  roads  treated  with 
many  asphaltic  oils. 

Failures  of  Bituminous  Surfaces.  The  causes  of  failure  of 
bituminous  surfaces  are  numerous.  They  may  be  considered 


* 


FIG.  92.     Failure  of  Asphaltic  Oil  Mat  Surface  Due  to  Poor  Adhesion  Caused 
by  Oil  Being  Applied  to  Damp  Surface. 

from  the  standpoint  of  the  condition  and  character  of  the  original 
surface,  the  material  used,  the  method  of  construction,  and  local 
conditions. 

Condition  of  Surface.  The  failure  of  bituminous  surfaces  from 
the  standpoint  of  the  character  of  the  original  surface  is  many 
times  due  to  failure  on  the  part  of  those  in  charge  to  place  the 
surface  in  satisfactory  condition  before  the  application  of  the 
bituminous  material.  Many  cases  are  noted  where  bituminous 
materials  are  applied  over  a  surface  in  which  are  found  many 
pot-holes  and  ruts,  or  which  is  dirty,  due  either  to  accumulated 
dust  and  dirt  or  to  the  original  method  of  construction.  In 
many  cases  a  damp  condition  of  the  surface  has  resulted  in 
failure.  (See  Fig.  92.) 


BITUMINOUS    SURFACES 


251 


Bituminous  Material.  From  the  standpoint  of»the  physical 
and  chemical  properties  of  the  material,  many  instances  may 
be  cited  in  which  failure  is  due  to  materials  not  having  the 
proper  characteristics  for  the  conditions  under  which  they  are 
employed.  The  large  percentage  of  volatile  constituents  con- 
tained in  certain  asphaltic  oils  has  rendered  surfaces  constructed 
with  them  unsatisfactory  because  of  the  long  period  required 


FIG.  93.     Failure  of   Bituminous  Surface   Due  to   Using  an  Excess  of 
Bituminous   Material. 

for  these  surfaces  to  "set  up"  so  that  the  bituminous  material 
will  not  track  or  the  carpet  thus  formed  will  not  creep  and 
form  waves  and  humps.  In  certain  cases  the  use  of  light  oils 
on  tar  or  asphalt  surfaces  has  softened  the  original  bituminous 
surface  to  such  an  extent  as  to  render  the  road  or  pavement 
unsatisfactory  for  use. 

Construction  Methods.  From  the  standpoint  of  construction, 
failures  are  due  both  to  the  use  of  too  small  an  amount  of  the 
bituminous  material  and  to  an  excess  of  material.  Fig.  93  shows 
the  effect  of  using  too  much  material.  Improper  application, 


252 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


resulting  in  uneven  distribution,  is  accountable  for  many  failures 
of  bituminous  surfaces,  while  in  other  cases  a  lack  of  sufficient 
covering  of  stone  chips  or  material  of  a  similar  character  has 
rendered  the  surface  sticky  and  mushy. 

Unsuitability.     There  are  numerous  instances  where  bitumi- 
nous surfaces  have  been  adopted  under  conditions  which  call 


FIG.  94.     Calk  Holes  in  a  Bituminous  Mat  Surface. 

for  the  construction  of  bituminous  concrete  pavements  or  even 
some  type  of  block  pavements.  A  mat  type  of  construction, 
which  has  been  employed  to  a  considerable  extent,  has  proved 
inefficacious  in  cases  where  the  amount  of  motor-car  traffic  was 
not  sufficient  to  iron  out  satisfactorily  the  calk  holes  caused  by 
the  horse-drawn  vehicle  traffic.  Fig.  94  shows  the  effect  of  the 
impact  of  horses'  feet  on  some  mat  surfaces. 


CHAPTER  XI 
BITUMINOUS  MACADAM  PAVEMENTS 

A  bituminous  macadam  pavement  is  "one  having  a  wearing 
course  of  macadam  with  the  interstices  filled  by  penetration 
methods  with  a  bituminous  binder."*  In  connection  with  the 
interpretation  of  this  definition  it  should  be  noted  that  the  term 
macadam  refers  to  "a  road  crust  composed  of  stone  or  similar 
material  broken  into  irregular  angular  fragments  compacted  to- 
gether so  as  to  be  interlocked  and  mechanically  bound  to  the 
utmost  possible  extent."  * 

DEVELOPMENT.  In  1820  a  bituminous  macadam  pavement, 
constructed  with  a  tar  cement,  was  laid  in  London.  The  pene- 
tration method  of  constructing  bituminous  pavements  has  been 
used  extensively  in  the  United  States  since  1908  in  building 
roads  and  residential  streets,  due  to  its  low  first  cost  and  the 
rapidity  with  which  it  may  be  constructed  with  proper  plant 
equipment  and  under  favorable  climatic  conditions. 

BITUMINOUS  MATERIALS 

The  bituminous  materials,  used  in  the  construction  of  bitu- 
minous pavements  built  by  penetration  methods,  include  asphalts, 
heavy  asphaltic  oils,  refined  water-gas  tars,  refined  coal-gas  tars, 
combinations  of  refined  tars,  and  combinations  of  refined  tars 
and  asphalts. 

CONSTRUCTION 

SUBGRADE.  The  subgrade  for  bituminous  macadam  pave- 
ments should  be  prepared  in  accordance  with  the  principles  out- 
lined in  Chapter  V. 

METHODS  OF  CONSTRUCTION  WITH  BROKEN  STONE.  In  the 
construction  of  bituminous  macadam  pavements  it  is  desired 

*  Dec.,  1914  Proceedings,  Am.  Soc.  C.  E.,  pages  3011  to  3016. 

253 


254  ELEMENTS   OF  HIGHWAY  ENGINEERING 

to  secure,  (i)  a  stable  wearing  course  consisting  of  broken 
stone  or  similar  material  thoroughly  rolled  so  that  it  will  be 
well  compacted  and  keyed  together  and  with  the  several  sizes 
of  material,  uniformly  distributed,  and  (2)  a  uniform  distribu- 
tion and  penetration  of  the  bituminous  material  within  the 
upper  two  or  three  inches  of  the  crust.  Several  methods  of 
construction  have  been  devised  with  a  view  to  meeting  the 
above  prerequisites.  Due  to  lack  of  uniformity  in  the  den- 
sity of  the  wearing  course  of  broken  stone  and  in  the  amount 
of  bituminous  material  applied  per  square  yard  by  the  many 
methods  employed,  it  is,  however,  obvious  that  uniform  incor- 
poration of  the  binder  with  the  road  metal  is  difficult  to  secure. 

The  pavement  is  generally  built  in  two  or  three  courses,  the 
foundation  course  or  courses  being  from  4  to  8  inches  thick 
after  rolling,  and  the  top  course  from  2  to  3  inches  after  rolling. 
The  foundation  is  usually  composed  of  the  product  of  a  crusher 
which  passes  over  a  screen  with  i^-inch  circular  holes  and 
through  a  screen  with  2  ^2-inch  circular  holes,  or  over  a  2X-inch 
and  through  a  3^-inch  screen,  or  over  and  through  screens 
having  openings  of  similar  dimensions.  The  foundation  should 
be  thoroughly  compacted  with  a  10-  to  1 5-ton  roller  prior  to 
the  construction  of  the  wearing  course.  The  manner  of  finishing 
this  course  varies  in  the  several  methods,  as  will  be  noted  later. 

In  the  various  methods  of  constructing  the  wearing  course, 
the  bituminous  material  is  distributed  by  hand-pouring  appli- 
cations, gravity  distributors  and  pressure  distributors.  (See  Figs. 
95  and  96  and  also  distributors  described  and  illustrated  in 
Chapter  X.)  It  is  evident  that  uniform  application  of  the  bi- 
tuminous material  will  depend  upon  the  method  of  distribution 
employed.  To  secure  uniform  distribution  and  to  provide  for 
such  details  as  means  of  control  of  proper  pressure  and  temper- 
ature and  prevention  of  rutting  of  the  wearing  course  during 
construction,  the  American  Society  of  Municipal  Improvements 
prescribed  in  its  1914  specifications  the  following  requirements: 
"The  pressure  distributor  employed  shall  be  so  designated  and 
operated  as  to  distribute  the  bituminous  materials  specified  uni- 
formly under  a  pressure  of  not  less  than  twenty  (20)  pounds 


256 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


nor  more  than  seventy-five  (75)  pounds  per  square  inch  in  the 
amount  and  between  the  limits  of  temperature  specified.  It 
shall  be  supplied  with  an  accurate  stationary  thermometer  in 
the  tank  containing  the  bituminous  material  and  with  an  accu- 
rate pressure  gauge  so  located  as  to  be  easily  observed  by  the 
Engineer  while  walking  beside  the  distributor.  It  shall  be  so 


FIG.  96.     Ward  Pressure  Distributor.     (American  Machine.) 


operated  that,  at  the  termination  of  each  run,  the  bituminous 
material  will  be  at  once  shut  off.  It  shall  be  so  designed  that 
the  normal  width  of  application  shall  be  not  less  than  six  (6) 
feet  and  so  that  it  will  be  possible  on  either  side  of  the  machine 
to  apply  widths  of  not  more  than  two  (2)  feet.  The  distributor 
shall  be  provided  with  wheels  having  tires  each  of  which  shall 
not  be  less  than  eighteen  (18)  inches  in  width,  the  allowed 
maximum  pressure  per  square  inch  of  tire  being  dependent  upon 
the  following  relationship  between  the  aforesaid  pressure  and 
the  diameter  of  the  wheel:  For  a  two  (2)  foot  diameter  wheel, 
two  hundred  and  fifty  (250)  pounds  shall  be  the  maximum 
pressure  per  linear  inch  of  width  of  tire  per  wheel,  an  additional 
pressure  of  twenty  (20)  pounds  per  inch  being  allowed  for  each 
additional  three  (3)  inches  in  diameter." 


BITUMINOUS   MACADAM  PAVEMENTS  257 

The  crown  of  bituminous  macadam  pavements  should  not 
exceed  ^  inch  to  the  foot. 

Method  A.  The  wearing  course,  which  is  laid  on  the  founda- 
tion course  as  described  above,  consists  of  crusher-run  stone, 
ranging  in  size  from  1^4  to  ]/2  inch  in  longest  dimensions.  A 
typical  mechanical  analysis  of  this  type  of  crusher-run  stone 
follows : 

Passing     jkj-inch  screen  trace 

l/2.  18.9  percent 

y*  u      "    43.1 

V         i  "       34-4        " 

iK     "          "         3-6 

After  the  wearing  course  is  laid  the  bituminous  material  is  ap- 
plied, either  before  or  after  the  broken  stone  is  rolled,  some 
favoring  the  former  method  because  of  the  greater  depth  of 
penetration  secured.  The  wearing  course  should,  however,  be 
thoroughly  rolled  prior  to  the  application  of  the  bituminous 
material  in  order  to  secure  a  well  compacted  and  stable  course 
of  broken  stone,  mechanically  interlocked  and  bound  together. 
If  the  rolling  is  postponed  until  after  the  application  of  the 
bituminous  material,  the  wheels  of  the  roller  may  have  to  be 
wet  or  oiled  to  avoid  picking  up  the  surface.  When  the  wear- 
ing course  is  rolled  preceding  the  application  of  the  bituminous 
material,  a  coat  of  mineral  matter  is  spread  over  the  surface 
and  the  course  is  again  rolled.  In  certain  cases  this  method  is 
also  followed  where  the  upper  course  is  not  rolled  preceding  the 
application  of  the  bituminous  material.  The  necessity  of  a  seal 
coat  or  a  second  application  of  a  bituminous  material  is  deter- 
mined by  the  traffic  conditions.  The  surface  should  be  given 
a  seal  coat  if  it  is  to  be  subjected  to  a  heavy  combined  horse- 
drawn  vehicle  and  motor-car  traffic.  In  order  to  render  the 
surface  more  stable  and  less  affected  by  changes  in  tempera- 
ture, the  material  used  for  the  seal  coat,  in  some  cases,  has  a 
lower  penetration  ano^  a  higher  melting  point  than  that  used 
in  the  first  application.  Certain  asphalts  and  combinations  of 
asphalts  and  refined  tars,  semi-solid  at  normal  temperature,  have 
been  used  with  success  for  this  purpose.  The  total  amount  of 


258 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


bituminous  material  per  square  yard  used  in  this  method  varies 
from  2  to  3  gallons. 

Method  B.  In  case  the  metalling  of  the  upper  course  is  a 
uniform  product  of  about  i  or  i^  inches  in  size,  it  is  deposited 
in  a  layer  of  the  required  thickness  on  the  foundation  course 
and  lightly  rolled.  The  voids  are  greater  in  this  case  than  when 


FIG.  97.     Voids  of  Upper  Part  of  Foundation  Course  Being  Filled  with  Sand. 

the  wearing  course  of  Method  A  is  used,  hence  with  Method  B 
it  is  usually  practicable  to  secure  more  penetration.  The  course 
is,  however,  not  as  stable  as  that  of  Method  A.  The  bitumi- 
nous material  is  then  applied  in  an  amount  from  1^2  to  2  gallons 
per  square  yard  and  ^-inch  stone  chips  are  spread  on  the  sur- 
face and  thoroughly  rolled.  The  surface  is  next  broomed  with 
stiff  brooms,  removing  all  excess  chips,  and  another  coat  of 
bituminous  material,  from  ^  to  i  gallon  per  square  yard,  is 
applied,  covered  with  a  layer  of  stone  chips,  and  rolled.  This 
method  is  also  used  with  metal  of  the  upper  course  varying 
from  i>£  to  2^/2  inches,  in  which  case  ^-inch  stone  is  used  in 
place  of  ^-inch  chips. 

Method  C.     In  this  case  the  voids  in  the  upper  part  of  the 
foundation  course  are  filled  with  sand  or  small  sized  broken 


BITUMINOUS    MACADAM   PAVEMENTS  259 

stone.  (See  Fig.  97.)  After  rolling,  the  excess  samd  or  broken 
stone  is  broomed  off,  and  the  upper  course  of  metalling  is  spread 
and  lightly  rolled.  Coarse  sand,  stone  chips,  or  gravel  is  then 
spread  and  broomed  until  the  voids  of  the  metalling  are  filled  to 
the  surface.  The  bituminous  material  is  then  applied,  using 
from  i  to  ij/2  gallons  per  square  yard.  This  coat  is  covered 
with  a  layer  of  sand,  gravel,  or  screened  stone  chips,  and 
thoroughly  rolled.  'This  method  is  often  used  when  the  ma- 
terial composing  the  upper  surface  is  of  a  large  and  uniform 
size.  Sometimes  a  seal  coat  of  from  %  to  i  gallon  of  bituminous 
material  is  used  with  this  method. 

Method  D.  When  the  metalling  of, the  top  course  is  of  a 
large  and  uniform  size,  another  method  employed  is  to  place 
a  layer  of  sand  J^-inch  thick,  on  the  bottom  course,  the  voids 
of  which  have  been  filled.  The  bituminous  material  is  then 
distributed  on  this. layer,  using  about  i  gallon  per  square  yard. 
The  upper  course  of  metalling  is  immediately  placed  on  the 
mastic  and  rolled.  Continued  rolling  forces  the  material  of  the 
upper  course  down  and  draws  the  bituminous  mastic  up  into 
the  voids.  A  coat  of  bituminous  material  of  a  lower  penetra- 
tion, using  about  1^4  gallons  to  the  square  yard,  is  then  applied 
to  the  surface  of  the  upper  course.  A  layer  of  ^/6-inch  stone, 
}/2  to  ^  inch  thick,  is  spread  over  this  and  rolled.  The  work 
may  stop  here  or  may  be  carried  on  a  step  further  by  brooming 
off  the  excess  ^-inch .  stone,  afterwards  applying  another  coat 
of  bituminous  material,  l/2  gallon  per  square  yard,  adding  a  layer 
of  screened  stone  chips  and  rolling  the  same.  This  form  of 
construction,  when  refined  coal-gas  tar  is  used,  is  known  in  this 
country  as  the  "Modern  Pavement."  The  Gladwell  system,  as 
used  in  England,  is  essentially  the  same  in  principle  except  that 
a  course  of  screened  stone  chips  mixed  with  bituminous  material 
is  substituted  for  the  sand  layer  and  its  coat  of  bituminous 
material. 

Method  E.  A  bituminous  macadam  pavement  called  "Pitch- 
mac"  by  its  originator,  J.  A.  Brodie,  M.  Inst.  C.  E.,  City  En- 
gineer of  Liverpool,  has  been  used  in  England.  It  is  constructed 
on  a  foundation  of  stone.  The  wearing  course  of  broken  stone. 


260 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


varies  from  2  to  4^  inches  in  depth,  dependent  upon  traffic 
conditions.  If  the  wearing  course  is  from  2  to  3  inches  in  thick- 
ness, it  is  constructed  in  one  layer,  and  if  from  4  to  4^  inches, 
in  two  layers.  The  single  layer  and,  in  the  case  of  two  layers, 
the  upper  layer  is  composed  of  broken  stone  ranging  in  size 
from  1%  to  2>£  inches.  After  thorough  rolling  the  bituminous 
material  is  applied  to  the  single  layer  or  each  of  the  layers  of 


FIG.  98.     Construction  of  "Pitchmac"  Pavement  in  Liverpool. 

the  two-layer  wearing  course.  (See  Fig.  98.)  The  bituminous 
compound  consists  of  hot  sand  mixed  with  a  combination  of 
coal-tar  pitch,  refined  tar,  creosote  oil,  rosin,  and  Portland 
cement.  From  i^  to  2  gallons  per  square  yard  are  used  for 
the  one-layer  wearing  course  and  from  3^  to  3^  gallons  for 
two  layers.  To  assist  in  completely  filling  the  voids,  chips 
varying  in  size  from  ^  to  ^  inch  are  applied  during  the  rolling 
of  the  bituminous  grouted  layer. 

BITUMINOUS  GRAVEL  PAVEMENTS.  The  use  of  gravel  in 
the  construction  of  bituminous  pavements  by  penetration  meth- 
ods has  been  usually  limited  to  those  localities  where  broken 
stone  costs  more  than  gravel.  It  is  self-evident  that  it  is  im- 
practicable to  secure  the  same  keying  effect  with  gravel  as  can 
generally  be  obtained  with  broken  stone. 


BITUMINOUS   MACADAM  PAVEMENTS 


261 


COST  DATA.  The  cost  of  bituminous  pavements,  built  by 
penetration  methods,  varies  with  the  amount  and  kind  of  bitu- 
minous material  and  road  metal  used,  and  the  method  of  con- 
struction employed.  An  average  cost,  using  a  total  of  2  to  2j4 
gallons  of  bituminous  material  per  square  yard,  varies  from  25 
to  40  cents  per  square  yard  in  excess  of  the  cost  of  water-bound 
broken  stone  roads,  or  from  70  cents  to  $1.25  per  square  yard. 

In  the  following  table  are  given,  for  several  localities  through- 
out America,  the  average  1914  prices  of  bituminous  macadam 
pavements  and  foundations  constructed  with  various  total  thick- 
nesses of  broken  stone. 

From  Engineering  and  Contracting,  April  7,  1915 


City 

Square 
Yards 

Price* 
per 
Square  Yard 

Total 
Thickness, 
Inches 

Boston,  Mass    .           .            

176.  sen 

$0  8s 

6 

New  Haven,  Conn  ....      .  .           

ios,^8^ 

I  .OS 

6 

Passaic,  N.  J  
Cincinnati,  O    

15,612 

39.6S7 

0.92 
.  SI 

7 
9 

Gary,  Ind  

16,230 

33t 

10 

Chicago,  111  

S8o,S94 

-23t 

IQ/4 

Racine,  Wis  

7,614 

.69 

IO 

Kansas  City   Mo 

8q  4.16 

-JI 

IO 

Ottawa   Kansas 

21  062 

o  92! 

Q 

Nashville,  Tenn 

12  487 

o  08 

Q 

Los  Angeles,  Cal 

36O,OOO 

O   QO 

6 

St.  John,  N.  B  

15,586 

1.05 

6 

*  Price  covers  pavement,  foundation,  and  grading, 
f  Does  not  include  grading. 

MAINTENANCE 

The  maintenance  of  many  bituminous  macadam  pavements 
requires  covering  spots  with  sand,  gravel,  or  stone  chips,  where 
either  an  uneven  distribution  or  an  uneven  penetration  has 
caused  an  excess  of  bituminous  material  to  exude  on  the  surface. 
Places  which  disintegrate  should  be  cut  out  with  perpendicular 
sides  and  refilled  with  either  a  mixed  aggregate  or  by  building 
the  hole  up  with  successive  layers  of  road  metal  and  bituminous 
material,  the  former  method,  however,  giving  the  better  results. 
Light  oils  and  light  tars  should  never  be  used  for  repairing 


262  ELEMENTS   OF   HIGHWAY  ENGINEERING 

holes,  see  Fig.  99,  as  the  patches  thus  formed  will  not  be 
stable  and  hence  will  soon  be  displaced  by  traffic.  At  varied 
intervals  it  is  economical  to  renew  the  bituminous  surface  on 
the  pavement  by  using  from  %  to  ^  gallon  of  the  proper  type 
of  bituminous  material  per  square  yard.  It  will  be  found  that 


FIG.   99.     Improper   Method   of   Repairing  Holes.     Depressions  Filled  with 
Broken  Stone  and  Light  Oil. 

the  patrol  system  of  maintenance  will  materially  prolong  the 
life  of  the  pavement. 

CHARACTERISTICS 

ADVANTAGES.  The  advantages  incident  to  the  construction 
of  bituminous  surfaces  on  broken  stone  and  gravel  roads  enu- 
merated in  Chapter  X  are  also  characteristic  of  bituminous 
macadam  and  bituminous  gravel  pavements.  It  is  advisable 
to  emphasize  that  many  bituminous  pavements  constructed  by 
penetration  methods  possess  the  following  advantages :  suitability 
for  horse-drawn  as  well  as  motor-car  travel;  freedom  from  dust 
when  in  exposed  localities;  low  external  and  internal  wear  of 
road  metal;  low  cost  of  cleaning,  watering,  and  in  many  cases, 
of  repairs;  imperviousness  and  a  certain  degree  of  density  of 


BITUMINOUS   MACADAM   PAVEMENTS 


263 


the  wearing  course;   noiselessness  and  low  traction  with  certain 
types  of  bituminous  materials;   very  good  sanitary  qualities. 
DISADVANTAGES.      Among  the  disadvantages  attendant  upon 


FIG.  100.     Section  Showing  Uneven  Penetration. 


FIG.  101.     Example  of  Uneven  Distribution  of  Bituminous  Material. 

the  use  of  bituminous  macadam  and  gravel  pavements  should  be 
noted:  increase  in  cost  over  bituminous  surfaces  on  macadam 
and  gravel  roads;  slipperiness  when  some  bituminous  binders 
are  used  on  certain  grades;  dependence  upon  climatic  condi- 


264  ELEMENTS    OF   HIGHWAY   ENGINEERING 

tions  in  order  to  carry  on  construction  properly;  variability  in 
results  and  lack  of  uniformity  in  composition  of  wearing  sur- 
face secured,  due  to  uneven  penetration,  see  Fig.  100;  uneven 
distribution,  see  Figs.  101  and  102,  and  segregation  of  road  metal. 

CAUSES  OF  FAILURE.  The  causes  of  failure  of  bituminous 
macadam  and  bituminous  gravel  pavements  may  be  considered 
under  the  following  heads,  bituminous  material  and  methods 
of  construction. 

Bituminous  Material.  Unfortunately  many  are  the  instances 
where  unsuitable  bituminous  materials  have  been  employed. 
(See  Fig.  103.)  Many  engineers  having  charge  of  bituminous 
work  do  not  appreciate  the  fact  that  different  types  of  bitumi- 
nous materials  have  entirely  different  physical  properties  and 
require  entirely  different  treatment  in  use,  although  they  may 
have  been  purchased  under  one  and  the  same  specification  cover- 
ing chemical  and  physical  properties.  In  some  cases  entirely 
unjustifiable  combinations  of  materials  are  employed.  For  in- 
stance, in  one  case  an  asphalt  of  excellent  characteristics  was 
used  for  the  first  application,  while  for  the  second  application 
an  asphaltic  oil  having  decidedly  solvent  and  fluxing  properties 
was  employed.  The  result  is  shown  in  Fig.  104.  Overheating 
of  the  material  has  likewise  proved  the  cause  of  many  failures, 
as  the  properties  of  the  materials  are  sometimes  changed  and  in 
many  cases  the  materials  are  ruined. 

Methods  of  Construction.  Insufficient  rolling  has  caused 
many  failures.  Others  are  due  to  the  uneven  distribution  of 
the  bituminous  material  in  some  cases  when  horse-drawn  or 
power-driven  distributors  are  employed.  This  type  of  failure, 
however,  is  more  frequently  due  to  the  improper  use  of  hand- 
pouring  pots  and  hand-drawn  distributors.  Many  unsatisfac- 
tory bituminous  macadam  pavements  result  from  the  use  of 
the  wrong  sizes  of  broken  stone.  (See  Fig.  105.)  Failures 
due  to  the  rapid  formation  of  fine  cracks  caused  by  the  rocking 
movement  of  the  individual  stones  under  traffic,  finally  resulting 
in  ravelling  and  general  disintegration,  are  of  common  occur- 
rence. Segregation  of  sizes  of  stone  preventing  uniform  pene- 
tration results  in  "lean"  or  weak  spots  in  some  cases  and  "fat" 


FIG.  102.     An  Illustration  of  Uneven  Distribution  of  Bituminous  Material. 


I 


FIG.    103.     Surface  of  Soft   Broken  Stone  and  Asphaltic  Oil  Subjected  to 
Horse-drawn  Vehicle  Traffic. 


266 


ELEMENTS    OF   HIGHWAY  ENGINEERING 


spots  in  others.     In  certain  cases  after  a  rain  the  construction 
has  been  carried  on  before  the  broken  stone  immediatelv  below 


FIG.  104.     Result  of  Using  Improper  Combination  of  Bituminous  Materials. 


FIG.  105.     Surface  of  Large  Broken  Stone  Prior  to  Application  of  Bituminous 

Material. 

the  surface  has  dried  out.  Many  of  the  causes  attributed  to  the 
failures  of  bituminous  surfaces  may  likewise  apply  to  bitumi- 
nous macadam  and  bituminous  gravel  pavements. 


CHAPTER  XII 
BITUMINOUS  CONCRETE  PAVEMENTS 

"Bituminous  concrete  pavements  are  those  having  a  wearing 
surface  composed  of  stone,  gravel,  sand,  shell,  or  slag,  or  com- 
binations thereof,  and  bituminous  materials  incorporated  to- 
gether by  mixing  methods."  * 

DEVELOPMENT.  The  first  bituminous  concrete  pavement 
was  probably  constructed  about  1840  in  Nottingham,  England, 
while  in  the  United  States  the  first  construction  of  this  type 
of  pavement  was  at  Knoxville,  Tenn.,  in  1866.  From  1870  to 
1875  there  were  about  70,000  square  yards  of  bituminous  con- 
crete pavements  laid  in  Washington,  D.  C.  From  1888  to  1893 
many  yards  of  coal-tar  distillate  pavements  were  laid  in  Wash- 
ington because  Congress  had  prohibited  the  use  of  sheet  asphalt 
pavements  in  the  District  of  Columbia.  From  1880  to  1891 
several  sections  of  bituminous  concrete  pavements,  using  coal- 
tar  as  the  bituminous  cement,  were  laid  in  Ontario,  Canada. 
Another  early  bituminous  concrete  pavement  was  built  in  Con- 
cord, New  Hampshire,  and  is  still  in  use  to-day.  During  the 
closing  period  of  the  nineteenth  century  attention  was  directed 
in  England  to  the  details  of  construction  of  bituminous  concrete 
pavements  for  use  on  highways  outside  of  built-up  districts. 
In  the  United  States  at  the  opening  of  the  twentieth  century, 
Fred  J.  Warren  urged  the  use  of  bituminous  concrete  as  a  pave- 
ment for  streets  in  competition  with  sheet  asphalt,  wood  block, 
and  brick  pavements.  Based  on  experimental  work  during  1906, 
1907,  and  1908,  Rhode  Island  in  1909  was  the  first  State  to 
adopt  the  bituminous  concrete  pavement  as  a  standard  type  of 
construction  for  use  on  state  highways.  Since  1910  there  has 
been  a  rapidly  growing  appreciation  of  the  inherent  value  of 
the  many  different  types  of  bituminous  concrete  pavements  for 

*  Dec.,  1914  Proceedings,  Am.  Soc.  C.  E.,  page  3011. 
267 


268 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


use  on  roads  and  streets.  Instances  of  development  in  this 
field  of  construction  will  be  cited  later,  in  connection  with  each 
of  the  types  of  bituminous  concrete  pavements. 

MINERAL  AGGREGATES 

Bituminous  concrete  pavements  differ  principally  in  the  char- 
acter of  the  mineral  aggregate  and  the  kind  of  bituminous 
material  of  which  the  wearing  course  is  composed.  Leaving  out 
of  consideration  sheet  asphalt,  bituminous  concrete  pavements 


Courtesy  of  V/m.  H.  Connell. 

FIG.  1 06.     Cross-section  Bituminous  Concrete  Pavement.     Class  i.  B. 

may  be  divided  into  the  following  classes  and  subdivisions  based 
upon  the  character  of  the  mineral  aggregate  employed. 

CLASS  i.    Mineral   aggregates   composed   of   broken   stone, 
either  alone  or  in  combination  with  sand. 

A.  Broken  stone  composing  one  product  of  a  crushing  plant. 

B.  Combinations  of  broken  stone  composing  one  product 
of  a  crushing  plant  and  fine  mineral  matter,  such  as  sand  or 
stone  screenings.     (See  Fig.  106.) 

C.  Mechanically  graded  aggregates  of  broken  stone,  either 
alone  or  combined  with  sand,  with  or  without  other  mineral 
matter. 

CLASS  2.    Mineral  aggregates  composed  of  gravel  or  gravel 
and  sand. 

A.     Run  of  the  gravel  bank. 


BITUMINOUS   CONCRETE   PAVEMENTS  269 

B.     Combinations  of  screened  sizes. 

CLASS  3.  Mineral  aggregates  composed  of  such  materials  as 
slag,  shell,  or  cinders. 

CLASS  i.  A.  Pavements  of  this  type  have  been  constructed 
of  one  or  more  courses  of  bituminous  coated  metal  with  and 
without  seal  coats  of  bituminous  materials.  During  the  period 
from  1869  to  1875  many  patents  were  granted  by  the  United 
States  Government  covering  bituminous  concrete  of  this  type. 

Patent  No.  114,172,  granted  to  F.  E.  Mathews  in  1871,  con- 
tains the  following  description  of  a  two-layer  bituminous  concrete 
pavement : 

"When  laid  on  an  ordinary  foundation  the  concrete  should 
be  laid  in  two  layers  or  coats  and  should  be  from  6  to  8  inches 
thick  when  finished. 

"For  the  first  layer  the  stone  used  in  making  the  concrete 
may  be  such  as  would  pass  through  a  screen  having  a  3-inch 
mesh;  about  six  measures  of  the  stone  should  be  mixed  with 
one  measure  of  the  asphalt  mixture  and  this  layer  should  be 
about  4  inches  thick. 

"For  the  second  layer  or  coat  the  stone  should  pass  through 
a  screen  having  a  i^-inch  mesh,  and  be  mixed  with  the  asphalt 
mixture  in  the  proportion  of  about  four  parts  of  the  former  to 
one  part  of  the  latter,  and  the  second  layer  should  be  from 

2  to  3  inches  thick. 

"Fine  sand  or  any  suitable  fine  hard  substance  may  be 
sprinkled  over  the  last  coat  just  before  or  after  rolling,  to 
give  the  pavement  a  smooth  compact  surface." 

Many  descriptions  of  old  pavements  of  this  type  may  be 
found  in  technical  literature.  As  an  illustration  may  be  cited 
the  following  specification  used  in  England  in  the  latter  part  of 
the  nineteenth  century:  "The  hot  stone,  when  ready  for  mixing, 
is  screened  into  material  of  three  sizes,  i  to  2  inches  for  the 
body,  Y2  to  i  inch  for  the  intermediate  coat,  and  ^4  to  ^  inch 
for  the  top  dressing.  The  coarsest  material  is  used  in  a  layer 

3  to  4  inches  thick,  the  intermediate  size  forms  a  coat  of  about 
^4  of  an  inch,  and  the  top  dressing  is  used  in  the  thinnest  layer 
possible,  with  a  view  to  filling  all  interstices.   Afterward  a  dressing 


270  ELEMENTS   OF  HIGHWAY  ENGINEERING 

of  ^4-inch  and  smaller  granite  screenings  is  scattered  broadcast, 
and  the  traffic  at  once  allowed  on  the  road  to  work  this  top 
dressing  into  the  tarred  material.  Each  of  the  layers  is  rolled 
separately  with  a  lo-ton  roller." 

Naturally,  Class  i.  A.  has  been  very  popular,  due  to  its  sim- 
plicity.    Excellent  pavements  have  been  constructed  by  this 


FIG.  107.  Upper  Part,  Water-bound  Broken  Stone  Road.  Lower  Part, 
Bituminous  Concrete  Pavement,  Class  I.  A.,  without  Seal  Coat,  Rhode 
Island  State  Highway. 

method  where. the  aggregate  consisted  of  one  product  of  a  stone- 
crushing  plant  having  the  following  characteristics  based  upon 
a  mechanical  analysis:  all  the  stone  passed  a  i^-inch  screen; 
not  over  25  percent  passed  a  i^-inch  screen  and  was  retained 
on  a  ^-inch  screen;  and  not  over  5  oercent  passed  a  >^-inch 
screen. 

The  State  Board  of  Public  Roads  of  Rhode  Island  has  used 
Class  i.  A.  since  1906.  (See  Fig.  107.)  The  road  metal  was 
furnished  under  the  following  specification:  "The  bottom 
course  shall  consist  of  stone  from  i  inches  to  2  inches  in 


BITUMINOUS   CONCRETE  PAVEMENTS  271 

their  longest  dimensions,  the  upper  course  of  stgne  from  %  to 
i^  inches  in  their  longest  dimensions."  The  product  of  the 
crusher  which  met  this  specification  for  the  stone  of  the  wear- 
ing surface  was  obtained  from  the  ordinary  type  of  crushing 
plant,  the  broken  stone  usually  passing  over  a  y^-  to  ^-inch 
screen  and  through  a  ij^-inch  screen.  A  mechanical  analysis 
of  a  typical  product  used  in  Rhode  Island  is  given  below. 

Percent  passing  lo-mesh  sieve I  .o 

screen 2.5 

"      30-8 

;;  34.2 

23.4 

" 8.1 

CLASS  i.  B.  This  type,  that  is,  one  having  an  aggregate 
which  is  a  combination  of  broken  stone  composing  one  product 
of  a  stone-crushing  plant  mixed  with  fine  material,  such  as 
sand,  screenings,  or  material  of  a  similar  character,  has  been 
described  many  times  in  early  technical  literature.  For  example, 
the  following  description  was  published  over  thirty  years  ago: 
"The  manner  of  preparing,  treating,  and  laying  the  asphalt 
mass  is  as  follows:  He  took  asphalt,  one  hundred  and  twenty- 
five  parts;  petroleum-oil,  twenty-five  parts.  These  substances 
were  melted  and  thoroughly  incorporated  together,  and  to  this 
mixture  he  added,  in  a  heated  state,  sand  or  powdered  stone, 
750  parts,  and  gravel  or  broken  stone,  also  heated,  1,100  parts. 
The  whole  was  then  thoroughly  mixed." 

Pavements  of  this  type  have  been  used  by  many  engineers. 
In  Washington,  D.  C.,  bituminous  concrete  pavements  have 
been  constructed  in  accordance  with  the  following  specifications 
covering  the  mineral  aggregate:  "The  paving  material  shall  be 
composed  of  crushed  trap  rock  screenings,  concrete  sand,  and 
mineral  dust  in  the  following  proportions:  Trap  rock  screen- 
ings, two  parts;  concrete  sand,  one  part,  and  mineral  dust,  at 
least  5  percent  of  the  above  aggregate;  mixed  with  asphaltic 
cement."  The  trap  rock  screenings  referred  to  above  varied  in 
size  from  i  inch  to  screenings  and  were  devoid  of  dust.  De- 
tailed specifications  were  given  also  with  reference  to  the  char- 
acter of  the  sand  and  the  mineral  dust. 


272  ELEMENTS   OF   HIGHWAY   ENGINEERING 

CLASS  i.  C.  Specifications  for  pavements  of  this  type  call 
for  mechanically  graded  aggregates  of  broken  stone,  either  alone 
or  combined  with  sand,  with  or  without  other  mineral  matter. 
From  a  historical  standpoint  reference  is  made  to  the  descrip- 
tion of  the  "Excelsior  Pavement,"  as  it  includes  the  charac- 
teristic features  of  this  class,  namely,  that  "several  sizes  are 
mixed  to  form  a  close  mass  without  cavities."  This  description 
is  made  up  of  pertinent  abstracts  from  a  book  entitled  "The 
Excelsior  Pavement,"  the  advertisement  of  which  is  dated  1871. 

"The  Excelsior  Pavement  consists  of  a  broken  stone,  or 
McAdam  base,  covered  with  a  concrete  surface,  which  being 
close,  smooth,  and  coherent,  presents  but  little  resistance  to 
travel,  and  permits  no  movement  among  the  stones  that  com- 
pose it;  therefore,  scarcely  any  dust  or  mud  is  formed;  its 
superiority  over  others  is  manifest. 

"The  resisting  material  may  be  sand  for  the  surface,  gravel 
or  broken  stone  mixed  with  sand  for  the  middle,  and  larger 
stone  for  the  bottom,  or  bed;  broken  stone  alone  is  preferred, 
sizes  being  chosen  which  best  form  a  compact  structure,  smooth 
on  top,  and  strong  throughout.  Small  fragments  are  not  gener- 
ally required.  Several  sizes  are  mixed  to  form  a  close  mass 
without  cavities,  the  coarser  stone  being  put  beneath.  This 
material  should  be  carefully  selected  for  its  strength  and  resist- 
ance, and  contain  no  dirt  or  other  foreign  matter. 

"The  sand,  gravel,  or  broken  stone  (of  different  degrees  of 
coarseness,  as  laid  at  or  below  the  surface)  should  be  sharp, 
clean,  and  hard;  the  cement  should  be  uniform,  fluid  and  ad- 
herent during  mixture;  and  the  compound  should  condense  and 
harden  rapidly  under  manipulation;  being  composed  of  the 
greatest  amount  of  rock,  and  the  least  of  cement,  which  will 
form  a  mass  most  resembling  stone  itself." 

In  1907  the  author  discovered  a  printed  specification  in  the 
Library  of  the  American  Society  of  Civil  Engineers  entitled 
"Specifications  for  the  Excelsior  Pavement."  The  following  ex- 
cerpt covers  the  description  of  the  mineral  aggregate: 

"Broken  stones  are  preferred  for  the  whole  pavement,  and 
shall  alone  be  used  for  the  covering.  The  greatest  dimension  of 


BITUMINOUS   CONCRETE  PAVEMENTS  273 

stones  for  the  base  (except  as  hereinafter  noted)  shall  be  be- 
tween 3  inches  and  %  inch,  and  for  the  covering  between  2 
inches  and  /{0  of  an  inch;  the  sizes  shall  be  mixed  in  propor- 
tion, varying  with  the  size  to  form  a  close  mass,  which,  when 
dry  and  compact,  can  absorb  not  more  than  20  percent  of 
water." 

It  is  evident  that  the  definition  of  bituminous  concrete  pave- 
ments of  Class  i.C.  covers  many  different  combinations  of  sizes 
of  road-metal  used  for  the  mineral  aggregate  of  the  wearing 
surface.  Some  of  the  combinations  in  use  will  be  described. 

Specifications,  Topeka.  Since  1911  many  thousands  of  yards 
of  pavement  of  Class  i.  C.  have  been  laid  under  the  so-called 
"Topeka"  specifications.  A  decree  was  signed  in  1910  by  cer- 
tain city  officials  and  representatives  of  the  Warren  Brothers 
Company  covering  the  use  of  the  "Topeka"  mineral  aggregate. 
The  following  quotation  is  from  the  decree  to  which  reference 
has  been  made:  "It  appearing  to  the  court  that  of  the  mineral 
matter  used  in  the  pavements  actually  constructed  in  the  cities 
of  Topeka  and  Emporia,  Kansas,  no  particles  of  stone  were 
used  that  would  not  pass  a  screen  with  openings  ^  inch  in 
diameter,  and  that  less  than  10  per  cent  of  the  stone  or  coarse 
sand  used  would  be  retained  upon  a  screen  with  openings  ^  inch 
in  diameter,  and  the  remaining  mineral  matter  used  being  finer 
than  l/^  inch:  and  it  further  appearing  that  pavements  con- 
structed by  the  use  of  mineral  particles  as  above  described  do 
not  infringe  the  claims  of  complainant's  patent  No.  727,505, 
sued  upon  in  this  case;  .  .  .  And  it  further  appearing  that  the 
pavements  as  actually  constructed  in  the  cities  of  Topeka  and 
Emporia,  Kansas,  do  not  infringe  the  claims  of  complainant's 
patent  No.  727,505,  sued  upon  in  this  case,  and  that  any  pave- 
ments hereafter  constructed  in  substantial  compliance  with  the 
following  formula,  to  wit: 

"  Bitumen,  from  7  percent  to  n  percent. 

Mineral  aggregate,  passing  2OO-mesh  screen,  from    5  percent  to  n  percent. 
40       "  18     "    '       "  30    ' 

10       "         <(  "     25     "    "     "  55    " 

4       "         «  «       8     "    "     "  22    "     " 

"  "  "2       "         "         less  than  10  percent. 


274  ELEMENTS   OF  HIGHWAY  ENGINEERING 

Sieves  to  be  used  in  the  order  named  would  not  infringe  the 
claims  of  said  patent." 

Specifications,  Asphalt  Block.  For  many  years  a  bituminous 
concrete  having  the  essential  features  of  the  "Topeka"  grading 
has  been  used  in  the  form  of  asphalt  blocks.  The  following 
specifications  were  adopted  in  1911  by  the  Association  for  Stand- 
ardizing Paving  Specifications: 

"The  size  of  the  block  shall  be  12  inches  long,  5  wide  and 
3  deep.  Blocks  exceeding  the  following  limits  of  permissible 
variation  from  the  above  measurements  will  be  rejected:  Length 
from  ii  ^i  to  i2}4  inches,  width  from  4%  to  5//6  inches,  depth 
from  2*/{6  to  3/{6  inches.  The  blocks  shall  be  composed  of 
asphalt  cement,  filler,  and  crushed  trap  rock  or  hard  limestone. 

"The  filler  shall  be  thoroughly  dry  limestone  dust  or  Portland 
cement,  the  whole  of  which  shall  pass  a  30-mesh  per  linear  inch 
sieve,  85  percent  shall  pass  a  ico-mesh  per  linear  inch  sieve, 
and  at  least  66  percent  shall  pass  a  2oo-mesh  per  linear  inch 
sieve.  Not  less  than  7  percent  of  this  filler  shall  be  used  in 
the  mixture  from  which  the  blocks  are  made.  The  crushed 
rock  used  shall  be  of  good  quality  of  freshly  crushed  hard  trap 
rock  or  hard  limestone  free  from  all  weathered  and  other  soft 
material.  It  must  be  clean  and  free  from  any  adhering  dust, 
clay,  or  other  foreign  matter. 

"The  asphalt  cement,  dust,  and  rock  shall  be  thoroughly 
mixed  while  hot  in  such  proportions  as  to  give  a  block  contain- 
ing not  more  than  8.5  percent  or  less  than  5.5  percent  of  bitu- 
men soluble  in  carbon  disulphide,  and  at  least  12  percent  of 
mineral  matter  passing  a  2oo-mesh  sieve." 

Specifications,  Bitulithic.  Since  the  beginning  of  the  twenti- 
eth century  a  large  amount  of  a  proprietary  pavement  known 
as  "Bitulithic"  has  been  laid  in  the  United  States.  As  described 
by  Fred  J.  Warren,  the  wearing  surface,  which  usually  has  a 
thickness  of  about  2  inches  after  compression,  is  constructed  as 
follows:  "The  mineral  or  stone  part  is  dried  and  heated  in  a 
modern  dryer  and  is  then  separated  by  screening  with  a  rotary 
screen  into  its  sizes,  varying  from  fine  dust,  which  is  less  than 
J/2oo  of  an  inch  in  diameter,  to  the  largest  size  used.  The  several 


BITUMINOUS   CONCRETE  PAVEMENTS  275 

sizes  of  stone  are  then  mixed  in  predetermined 'proportions,  so 
as  to  reduce  the  voids. to  about  10  percent,  in  a  modern  'twin 
pug'  steam  power  mixer,  and  the  hot  bituminous  cement  is 
added  in  the  mixer  in  sufficient  quantity  to  not  only  coat  every 
particle  and  fill  all  of  the  remaining  voids  but  with  enough 
surplus  to  furnish  to  the  mixture  after  compression  a  rubbery 
and  slightly  flexible  condition." 

Specifications  proposed  by  the  Warren  Brothers  Company 
covering  the  aggregate  are  cited. 

"Mineral  Aggregate.  Upon  the  roughened  surface  of  the  con- 
crete prepared  as  above  specified  there  shall  be  laid  the  fol- 
lowing wearing  surface  composed  of  hard,  crushed  stone,  sand, 
and  bituminous  cement  to  have  the  thickness  when  compressed 
of  2  inches. 

"In  preparing  the  mineral  aggregate  for  the  above  wearing 
surface  the  following  method  and  apparatus  shall  be  used:  The 
maximum  size  stone  should  be  about  one-half  the  thickness  of 
the  wearing  surface.  The  several  grades  and  sizes  of  mineral 
aggregate  shall  be  accurately  measured  in  proportions  previously 
determined  by  laboratory  tests  to  give  the  best  results,  that  is, 
the  most  dense  mixture  of  mineral  aggregate  and  one  having 
inherent  stability,  heated  in  a  rotary  mechanical  heater,  so  de- 
signed as  to  keep  each  batch  by  itself  until  heated,  and  then 
pass  into  a  rotary  mixer;  or  the  varying  sizes  of  stone  approxi- 
mately proportioned  shall  be  fed  into  an  elevator  terminating 
and  discharging  into  a  rotary  dryer,  and  after  heating,  the  stone 
shall  be  elevated  and  passed  through  a  rotary  screen  having 
sections  with  various  sized  openings.  The  minimum  screen  open- 
ing shall  be  I/i0  inch  and  the  maximum  shall  not  be  greater 
than  ij/z  inch.  The  difference  in  the  width  of  openings  in  suc- 
cessive sections  shall  not  exceed  %  inch  in  sections  having 
openings  smaller  than  ]/%  inch  and  shall  not  exceed  %  inch  in 
sections  having  openings  greater  than  ^  inch.  The  several 
sizes  of  stone  thus  separated  by  the  screen  sections  shall  pass 
into  a  bin  containing  sections  or  .compartments  corresponding 
to  the  screen  sections.  From  these  compartments  the  stone 
shall  be  drawn  into  a  weigh  box,  resting  on  a  multi-beam  scale. 


276  ELEMENTS    OF  HIGHWAY   ENGINEERING 

The  several  sizes  of  mineral  aggregate,  after  being  separately 
weighed  or  measured  as  above,  shall  be  dropped  into  a  'twin 
pug'  or  other  approved  form  of  mixer.  In  the  mixer  bitulithic 
cement  shall  be  added  in  sufficient  quantity  to  coat  all  particles 
and  fill  such  voids  as  remain  unfilled  by  the  proportionment  of 
the  mineral  aggregate.  The  aggregate  shall  be  so  proportioned 
as  to  secure  in  the  aggregate  inherent  stability,  density,  free- 
dom from  voids,  and  resistance  to  displacement,  and  a  mixture 
which  when  combined  with  the  bitulithic  cement  and  compacted 
together  will  form  a  bituminous  street  pavement  structure  con- 
taining mixed  mineral  ingredients  of  such  grades  as  to  give  the 
structure  inherent  stability,  and  one  in  which  the  largest  and 
smallest  pieces  are  associated  with  each  other  indiscriminately 
throughout  the  structure,  and  in  which  the  plastic  bituminous 
composition  permeates  the  entire  mass,  uniting  the  various  sized 
particles  thereof;  filling  the  voids  and  forming  the  wearing  sur- 
face. If  the  crushed  stone  does  not  contain  enough  finely  divided 
particles  to  fill  the  small  voids  in  the  aggregate  the  deficiency 
of  these  finely  divided  particles  shall  be  made  up  by  the  addition 
of  sand  or  other  suitable  fine  mineral  matter." 

CLASS  2.  Mineral  aggregates  of  this  type  are  composed  of 
gravel,  either  run  of  the  bank  or  graded  mixtures  of  gravel 
and  sand.  Unless  finished  with  an  adequate  seal  coat,  the  fine 
gravel  of  the  surface  is  liable  to  be  dislodged  if  the  traffic  in- 
cludes horse-drawn  vehicles.  It  is  also  evident  that  the  inter- 
locking of  broken  stone  upon  which  the  stability  of  many  types 
of  pavements  depends  is  a  desideratum  which  is  very  difficult  to 
obtain  with  a  gravel  aggregate. 

CLASS  3.  A  mineral  aggregate  of  slag  has  been  used  to  a 
considerable  extent  in  England  since  1900.  Although  laid  by 
various  municipalities,  the  largest  amount  has  been  used  in 
connection  with  the  construction  of  "Tarmac."  One  of  the 
"Tarmac"  plants  is  located  at  Wolverhampton,  adjacent  to  that 
of  a  company  producing  large  quantities  of  blast-furnace  slag. 
The  large  molds  of  slag  are  transported  by  small  cars  from 
the  iron  works  on  a  narrow  gauge  track  and  dumped  near  the 
"Tarmac"  works  and  allowed  to  cool.  These  large  blocks  are 


BITUMINOUS   CONCRETE  PAVEMENTS  277 

broken  by  sledge-hammers  to  a  size  suitable  for»the  crusher,  to 
which  point  the  broken  slag  is  taken  by  an  inclined  railway. 
It  is  crushed  and  screened  into  sizes  varying  from  y^  to  2^ 
inches  and  dropped  into  bins  and  thence  into  a  mixing  machine, 
where  it  is  mixed  with  a  tar  compound.  Since  the  slag  is  warm 
even  after  it  has  been  crushed,  no  heating  preliminary  to  mixing 
is  necessary. 

A  large  amount  of  "Tarmac"  has  been  used  in  the  County 
of  Nottingham.  None  of  the  roads  are  painted  when  constructed. 
They  present  an  excellent  non-slippery  mosaic  surface.  The 
maximum  grade  on  which  this  material  has  been  used  in  this 
locality  is  i  in  30.  The  pavements  are  built  in  two  courses  of  a 
total  thickness  of  4%  inches  and  with  a  standard  crown  of  J/^ 
inch  to  the  foot.  The  lower  course  is  2 finches  in  thickness, 
composed  of  pieces  of  slags,  ranging  from  *L%  to  2^  inches  in 
size,  and  the  upper  course  is  i$4  inches  in  thickness,  composed 
of  pieces  of  slag  ranging  from  %  to  i^  inches  in  size.  The 
cost  complete  averages  about  85  cents  per  square  yard. 

In  certain  cases  more  than  two  layers  of  bituminous  coated 
slag  are  employed.  The  construction  of  one  pavement  of  this 
type  will  be  described.  The  location  of  the  road  was  the  main 
shore  boulevard  at  Brighton-on-Sea  on  the  south  coast  of  Eng- 
land. The  details  of  construction  follow:  On  a  well-compacted 
gravel  foundation  was  spread  a  scattering  of  bituminous  coated 
chips;  the  bottom  layer,  composed  of  3^  inches  loose  of  i^- 
to  2^-mch  bituminous  coated  slag,  was  rolled ;  the  second  course 
consisted  of  2^  inches  loose  of  ^-  to  i^-inch  bituminous 
coated  slag,  which  course  was  thoroughly  compacted;  the  third 
course  was  composed  of  >2-inch  of  %-  to  >^-inch  bituminous 
coated  slag  chips,  which  layer  was  thoroughly  rolled;  the  pave- 
ment was  finished  by  rolling  a  top  dressing  of  uncoated  slag 
screenings. 

BITUMINOUS  MATERIALS 

BITUMINOUS  CEMENTS.  The  bituminous  materials  used  in 
the  construction  of  bituminous  concrete  pavements  are  asphalts. 


278  ELEMENTS   OF  HIGHWAY  ENGINEERING 

refined  water-gas  tars,  refined  coal  tars,  combinations  of  tars, 
and  combinations  of  tars  and  asphalts. 

BITUMEN  CONTENT  IN  WEARING  COURSE  MIXTURES.  In 
specifications  and  records  of  work  the  bitumen  content  is  ex- 
pressed in  one  of  two  ways:  first,  as  the  number  of  gallons  per 
square  yard  or  cubic  yard  of  mineral  aggregate;  and,  second, 
as  a  certain  percentage  by  weight  of  the  wearing  course  mixture. 
It  is  apparent  that  the  volumetric  amount  of  bituminous  cement 
used  by  the  second  method  materially  depends  upon  the  specific 
gravities  of  both  the  mineral  aggregate  and  the  bituminous 
cement.  The  problem  thus  presented  to  the  engineer  during 
construction  and  to  the  chemist  in  reporting  upon  an  analysis  of 
a  wearing  course  mixture  has  been  considered  by  Prevost  Hub- 
bard,  and  is  briefly  discussed  in  the  following  abstracts  of  a 
paper  by  him.* 

"An  engineer  who  superintends  the  construction  of  a  bitu- 
minous road  or  pavement  can,  of  course,  state  the  volume  pro- 
portions of  the  constituents  which  he  uses  in  a  given  mix,  but 
if  the  bituminous  material  contains  considerable  mineral  matter, 
or  organic  matter  not  bitumen,  he  encounters  a  serious  diffi- 
culty in  stating  the  actual  proportions  of  aggregate  and  bitumen. 
On  the  other  hand,  the  chemist  who  examines  a  mix  can  state 
the  weight  proportions  of  aggregate  and  bitumen,  but  will  often 
be  unable  to  determine  the  exact  volume  proportions  in  cubic 
yards  and  gallons  used,  owing  to  considerable  variations  in  the 
volume  of  a  unit  weight  of  aggregate  in  different  stages  of  com- 
paction. If  the  bituminous  material  originally  used  contains  an 
unknown  amount  of  mineral  matter  or  organic  matter  not  bitu- 
men, he  may  also  be  unable  to  determine  accurately  the  pro- 
portions (either  by  weight  or  by  volume)  of  the  original  con- 
stituents which  entered  into  the  mix. 

"While  the  subject  would  seem  to  be  in  a  more  or  less  chaotic 
condition  in  so  far  as  extreme  accuracy  is  concerned,  it  appears 
to  the  author  that  a  much  more  rational  basis  of  comparison 
is  possible  than  that  ordinarily  used.  He  would,  therefore,  sug- 

*  "The  Bitumen  Content  of  Coarse  Bituminous  Aggregates,"  Proceedings, 
VI  Congress  International  Association  for  Testing  Materials. 


BITUMINOUS    CONCRETE   PAVEMENTS 


279 


gest  that  in  the  examination  of  a  prepared  bituminous  mix  the 
chemist  always  report  the  specific  gravity  of  both  aggregate  and 
pure  extracted  bitumen  in  addition  to  the  usual  results.  If  this 
suggestion  is  followed  it  is  believed  that  an  intelligent  com- 
parison of  different  bituminous  mixes  can  be  made  with  little 
difficulty. 

"For  example,  we  may  consider  a  case  where  wide  variations 
exist  in  the  specific  gravity  of  both  aggregate  and  bituminous 
material  for  two  different  mixes.  For  a  basis  of  comparison  it 
may  be  assumed  that  the  two  aggregates  are  found  to  be  prac- 
tically identical  in  so  far  as  grading  is  concerned,  and  that  the 
percentage  by  weight  and  the  consistency  of  the  bitumens  are 
the  same.  According  to  the  ordinary  interpretation  of  results 
these  mixtures  would  be  equivalents.  If,  however,  it  is  found 
that  the  first  mix  is  composed  of  an  aggregate  with  a  specific 
gravity  of  2.50  while  the  extracted  bitumen  shows  a  specific 
gravity  of  1.17,  and  that  the  aggregate  of  the  second  mix  has  a 
specific  gravity  of  3.50  while  the  extracted  bitumen  shows  a 
specific  gravity  of  0.960,  the  percentage  of  each  constituent 
divided  by  its  specific  gravity  would  then  give  a  rational  volume 
proportion,  as  follows: 


Constituents 

Percent 
by  Wt. 

Specific 
Gravity 

%  Wt. 
Sp.  Gr. 

_    Rational 
Proportion 

Rational 
Percent 

First  mix: 
Aggregate  

Extracted  bitumen 

94 
6 

2.50 
I     17 

94_ 
2.50 
6 

=    37-6 

—          r     I 

88.0 
12    O 

Second  mix: 

100 

1.17 
94 

QT    n 

Aggregate  
Extracted  bitumen  

94 
6 

100 

3-5° 
0.96 

3-50 
6 

0.96 

=         6.3 

19.0 

"By  the  determination  of  what  has  been  termed  the  rational 
percent,  it  is  evident  that  the  first  mix  has  a  bitumen  equivalent 
of  about  two- thirds  that  of  the  .second  mix,  although  the  per- 
centages by  weight  are  the  same.  The  rational  variation,  7  per- 
cent, is  certainly  sufficient  to  mean  the  difference  between  success 
and  failure  for  certain  bituminous  aggregates. 


280 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


"In  conclusion,  it  may  be  stated  that  the  rational  percent 
of  bitumen  will  not  only  serve  as  an  improved  means  of  com- 
paring different  bituminous  aggregates  which  are  examined,  but 
may  be  used  to  advantage  in  calculating  in  advance  the  proper 
proportions  for  a  mix  if  the  properties  of  the  constituents  of 
the  mix  are  previously  determined." 

CONSTRUCTION 

SUBGRADE  AND  FOUNDATION.  The  subgrade  for  all  types 
of  bituminous  concrete  pavements  should  be  prepared  in  ac- 


FIG.  108.  Surface  of  Filled  Broken  Stone  Foundation  for  Wearing  Course  of 
Bituminous  Concrete,  Class  i.  A.,  Ashokan  Highway,  Board  of  Water 
Supply  of  the  City  of  New  York. 

cordance  with  the  principles  outlined  in  Chapter  V.  Satisfac- 
tory results  have  been  secured  under  certain  traffic  and  other 
local  conditions  by  using  a  broken  stone  foundation  course  vary- 
ing from  4  to  8  inches  in  depth  for  bituminous  concrete  pave- 
ments of  Classes  i.  A.  and  i.  B.  (See  Fig.  108.)  Commercial  traf- 
fic will  require  a  cement-concrete  foundation  course  for  these 
classes.  Where  Class  i.  C.  can  be  economically  employed,  the 
cement-concrete  foundation  will  be  required.  Large  sums  have 


BITUMINOUS   CONCRETE   PAVEMENTS  281 

been  wasted  by  laying  this  type  of  bituminous  concrete  pavement 
on  inadequate  foundations.  Bituminous  concrete  pavements  of 
Classes  2.  B.,  2.  C.,  and  3.  are  usually  laid  upon  foundation 
courses  composed  of  the  same  kind  of  road  metal  as  forms  the 
mineral  aggregate.  The  details  of  the  construction  of  foundation 
courses  of  various  types  have  been  explained  in  Chapter  V. 

WEARING  COURSE.  The  details  of  the  manufacture  and 
laying  of  the  wearing  course  will  depend  to  a  certain  extent 
upon  the  type  of  bituminous  concrete  pavement  employed  and 
the  kind  of  bituminous  cement  used.  There  are,  however,  cer- 
tain fundamental  methods  which  are  common  to  all  classes  of 
construction. 

The  mineral  aggregate,  consisting  of  one  or  more  grades  of 
broken  stone,  sand,  or  similar  materials  or  combinations  thereof, 


FIG.  109.  Surface  of  Compacted  Wearing  Course  of  Bituminous  Concrete, 
Class  i.  A.,  Ashokan  Highway,  Board  of  Water  Supply  of  the  City  of 
New  York. 


is  carefully  weighed  or  its  volume  determined  and  mixed  with 
a  given  weight  or  volume  of  bituminous  cement  in  a  type  of 
mixer  suitable  for  the  particular  class  of  aggregate  and  kind  of 
bituminous  cement  employed.  In  the  best  methods  of  construc- 
tion, the  mineral  aggregate  is  heated  prior  to  placing  it  in  the 


282 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


mixer.  The  aggregate  is  heated  to  a  temperature  which  will 
dry  it  and  allow  the  component  particles  to  be  readily  coated 
with  the  hot  bituminous  cement.  The  amount  of  bitumen 
employed  varies  from  5  to  8  percent  for  bituminous  concrete 
pavements  having  aggregates  composed  of  one  product  of  a 
stone-crushing  plant  to  7  to  n  percent  for  Topeka  bituminous 
concrete  pavements.  After  the  mineral  aggregate  is  thoroughly 


Courtesy  of  Mr.  Philip  P.  Sharpies. 

FIG.  no.     Application  of  Seal  Coat  on  Wearing  Course  of  Topeka  Bituminous 
Concrete  with  Pouring  Can  and  Squeegee. 

coated  in  the  mixer,  it  is  transported  by  wheel-barrows,  wagons, 
or  trucks  and  deposited  on  dumping  boards  which  have  been 
placed  upon  the  prepared  foundation.  The  bituminous  con- 
crete is  placed  by  shovels  and  raked  to  an  even  thickness  and 
is  then  thoroughly  compacted  by  rolling.  (See  Fig.  109.)  Many 
engineers  prefer  to  use  a  tandem  roller,  as  it  is  practicable,  under 
average  conditions,  to  shape  up  the  wearing  course  more  satis- 
factorily with  this  type  than  with  a  three-wheel  roller.  The 
weight  of  the  roller  used  varies  from  7  to  8  tons  for  Topeka 


BITUMINOUS    CONCRETE   PAVEMENTS 


283 


bituminous  concrete  to  9  to  1 2  tons  for  other  types«of  bituminous 
concrete  pavements. 

Seal  Coat.  After  the  bituminous  concrete  has  been  thor- 
oughly compacted  and  the  surface  is  dry  and  clean,  a  seal  coat 
is  applied  on  the  surface  of  many  types  of  pavements.  The 
bituminous  cement  is  distributed  by  using  pouring-pots,  see  Fig. 
no,  or  hand-drawn  gravity  or  pressure  distributors  followed  by 


FIG.  in.     Application  of  Seal  Coat  on  Wearing  Course  of  Bituminous  Con- 
crete,  Class   i.   A.,   with   Hand-drawn   Distributor  and   Squeegee. 

brushing  or  squeegeeing,  see  Fig.  in.  The  amount  of  seal  coat 
varies  from  about  J/&  of  a  gallon  per  square  yard,  if  used  on 
Topeka  bituminous  concrete  pavement,  to  from  }4  to  i  gallon 
per  square  yard  for  a  bituminous  concrete  pavement  having  an 
aggregate  composed  of  one  product  of  a  stone-crushing  plant. 
(See  Fig.  112.)  As  soon  as  practicable  a  thin  layer  of  clean,  dry 
stone  chips  is  applied  over  the  surface  of  the  seal  coat  and 
thoroughly  rolled. 

The  value  of  the  use  of  seal  coats  of  bituminous  materials 
on  bituminous  pavements  was  appreciated  by  some  of  the  pioneers 
in  this  field  of  highway  improvement.  In  a  book  entitled  "Bitu- 
minous Concrete  Pavements,"  published  in  1876,  N.  B.  Abbot 


284 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


presents   the  following  pertinent  discussion  on   this   detail  of 
construction : 

"It  is  the  practice  of  most  of  the  concrete-pavement  men 
to  finish  the  surface  with  a  top-dressing  of  dry  sand,  rolled  into 
the  surface;  or  of  hydraulic  cement,  swept  in  with  a  broom. 


m 


FIG.  112.  Surface  of  Seal  Coat  on  Wearing  Course  of  Bituminous  Concrete, 
Class  i.  A.,  Ashokan  Highway,  Board  of  Water  Supply  of  the  City  of 
New  York. 

I  became  early  satisfied  that  some  better  plan  of  finishing  was 
needed.  The  most  compact  concretes  are  more  or  less  porous 
on  the  surface;  and  though  these  pores  are  filled  with  the  sand 
or  cement  used  for  top-dressing,  neither  of  these  materials  being 
waterproof,  in  wet  weather  the  water  penetrates  the  pavement, 
street  dirt  mingles  with  the  water,  and  a  disintegrating  process 
begins,  which  soon  results  in  breaks  and  unevenness  of  surface. 
In  winter,  particularly,  the  moisture,  having  penetrated  the 
pavement,  freezes  and  thaws,  and  decay  is  hastened.  It  is  just 
as  essential  that  a  concrete  pavement  should  be  waterproof  as 
that  a  roof  should  not  leak.  My  experiments  in  this  direction 
resulted  in  what  is  known  as  the  Abbot  Grit  Surface,  which 
was  patented  June  17,  1873.  This  improvement  consists  in 
spreading  a  hot  liquid  composition  over  the  surface  of  the  pave- 


BITUMINOUS   CONCRETE   PAVEMENTS  285 

merit  after  it  is  rolled,  into  which  is  placed  clean,  dry  grit  or 
sand.  This  sand  is  immediately  rolled  into  the  surface  while 
the  composition  is  warm,  and  a  tough  coating  is  thereby  formed, 
which  not  only  prevents  the  pavement  from  being  slippery,  but 
effectually  closes  every  pore  in  the  surface,  and  makes  it  im- 
possible for  moisture  to  penetrate." 

In  1909  a  series  of  experimental  sections  was  constructed 
on  a  state  road  subjected  to  mixed  traffic  of  about  100  horse- 


FIG.  113.     Asphalt  Seal  Coat. 

drawn  vehicles  and  from  250  to  300  motor-cars  per  day,  many 
of  the  motor-vehicles  being  of  the  large  touring-car  type  and 
travelling  at  high  speeds.  These  experimental  sections  were 
constructed  to  determine  the  most  economical  and  satisfactory 
bituminous  material  to  be  used  for  the  cement  in  the  mix  and 
for  the  seal  coat  for  bituminous  concrete  pavements  subjected 
to  the  above  class  of  traffic.  Asphalt,  refined  water-gas  tar, 
refined  coal  tars,  and  combinations  of  refined  coal  tars  and 
asphalts  were  employed  in  the  construction  of  the  sections,  the 
same  material  being  used  for  the  binder  and  the  seal  coat.  The 
results  secured  from  these  experiments,  based  upon  an  exami- 
nation in  1912,  indicate  that  for  this  class  of  combination  traffic 
or  for  horse-drawn  vehicle  traffic  exclusively,  the  seal  coat  should 


286 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


consist  of  an  asphalt,  see  Fig.  113,  as  being  more  economical 
and   efficacious   than   refined  coal-gas  tar,  see  Fig.   114,   or    a 


FIG.  1 14.     Coal-Gas  Tar  Seal  Coat. 


FIG.  115.     Tar-Asphalt  Seal  Coat. 

combination  of  refined  tar  and  asphalt,  see  Fig.  115.  (Ice  covers 
a  portion  of  the  surface  shown  in  Figs.  113,  114,  and  115.) 
The  same  conclusion  has  been  reached  based  on  the  results  of 
experimental  sections  constructed  in  the  Borough  of  Queens  in 


BITUMINOUS    CONCRETE   PAVEMENTS  287 

191 1.  In  this  particular  instance  a  bituminous' concrete,  with 
tar  used  as  the  cement  and  seal  coat,  required  retreatment  with 
a  seal  coat  in  1912,  while  the  section  constructed  with  tar  as 
the  cement  and  asphalt  as  the  seal  coat  did  not  require  a  new 
seal  coat  when  inspected  in  1915. 

MANUFACTURE  AND  LAYING  OF  ASPHALT  BLOCKS.  Asphalt 
blocks,  as  heretofore  stated,  consist  of  a  hard  mineral  aggregate, 
a  filler  and  a  suitable  asphalt  cement.  It  has  been  found  that 
freshly  crushed  trap  rock  or  copper  conglomerate  makes  the 
most  satisfactory  and  durable  mineral  aggregate.  The  heated 
trap-rock,  filler,  usually  limestone  dust,  and  asphalt  cement  are 
mixed  in  a  pug-mill  mixer.  The  mixed  material  is  then  fed 
into  a  hydraulic  press,  where  it  is  subjected  to  a  pressure  per 
block  of  between  225  and  240  tons.  The  block,  after  being 
cooled  under  water,  is  ready  for  use.  Many  blocks  are  manu- 
factured in  standard  sizes  of  12  inches  long,  5  inches  wide,  and 
2,  2^,  and  3  inches  thick.  Before  the  blocks  are  shipped  they 
are  subjected  to  one  or  more  of  the  following  tests:  specific 
gravity,  penetration  of  block,  determination  of  percentage  and 
character  of  bitumen,  grading  of  mineral  aggregate,  and  water 
absorption.  The  Hastings  Pavement  Company  uses,  in  con- 
nection with  its  tests,  a  modified  form  of  the  Talbot- Jones-Smith 
brick  rattler,  as  shown  in  Fig.  116.  This  test  is  conducted  at 
temperatures  of  25°  F.  and  90°  F.  Fifty  pounds  of  cast-iron 
cubes  are  used  in  the  test  to  produce  a  pounding,  grinding  action 
on  the  ring  of  asphalt  blocks  which  is  bolted  in  the  cylinder  of 
the  machine.  The  rattler  is  run  for  10,000  revolutions.  The 
blocks  should  be  laid  in  a  cement-mortar  cushion,  y2  inch  in 
thickness,  covering  a  cement-concrete  foundation,  5  to  6  inches 
in  thickness,  and  rolled  with  a  9-  to  1 2-ton  tandem  roller.  (See 
Fig.  117.)  The  pavement  is  finished  by  brooming  sand  into  the 
joints  as  thoroughly  as  possible. 

MECHANICAL  APPLIANCES.  To  meet  the  demand  for  a  mix- 
ing plant  with  which  various  types  of  mineral  aggregates  can 
be  economically  heated  and  mixed  with  bituminous  material, 
several  machines  have  been  designed  in  the  United  States.  The 
requirements  of  engineers  vary  to  a  considerable  extent,  due  to 


Courtesy  of  the  Hastings  Pavement  Co. 

FIG.  116.     Talbot- Jones-Smith  Brick  Rattler  Used  in  Testing  Asphalt  Blocks. 


Courtesy  of  the  Hastings  Pavement  Co. 

FIG.  117.     Construction  of  Asphalt  Block  Pavement. 


BITUMINOUS   CONCRETE   PAVEMENTS 


289 


the  different  kinds  of  aggregate  and  bituminous  materials 
employed. 

Mixing  plants  may  be  divided  into  four  classes :  first,  cement- 
concrete  mixers;  second,  cement-concrete  mixers  with  heating 
attachments;  third,  dryers,  storage  bins,  and  mixers;  fourth, 
dryers,  storage  bins,  weighing  devices,  and  mixers. 

Cement-Concrete  Mixers.  Unheated  broken  stone  has  been 
mixed  with  tars  or  heavy  asphaltic  oils  in  the  ordinary  type  of 


FIG.  1 1 8.     "Smith"  Hot  Mixer. 

concrete  mixer.  With  this  type  of  plant  asphalt  cements  of 
low  penetration  at  normal  temperatures  cannot  be  mixed  with 
unheated  aggregates,  as  it  is  generally  impracticable  to  coat  the 
unheated  broken  stone  with  the  hot  asphalt  cement.  This  class 
of  mixers  should  not  be  used  for  the  construction  of  bituminous 
concrete  pavements. 

Cement-Concrete  Mixers  with  Heating  Attachments.  There 
are  several  different  types  of  this  class  of  mixing  plant  in  current 
use.  In  one  type,  see  Fig.  118,  the  heat,  in  the  form  of  hot  air, 
is  passed  into  the  mixer  by  means  of  a  large  iron  pipe,  which 
runs  from  the  fire-box  to  the  outlet  end  of  the  mixer.  A  second 
type,  see  Fig.  119,  consists  of  a  cylindrical  mixer  mounted  on  a 
four-wheeled  truck.  Heat  is  obtained  from  a  hot-air  jacket 


290  ELEMENTS   OF  HIGHWAY   ENGINEERING 

entirely  surrounding  the  cylinder  except  on  the  ends  and  by 
means  of  a  kerosene  torch  inserted  within  the  drum.  In  a  third 
type,  hot  air  obtained  by  the  combustion  of  oil  in  air  is  led 
from  the  combustion  chamber  into  the  mixing  cube.  After  the 
mineral  aggregate  is  heated  the  bituminous  cement  is  added. 


Courtesy  of  Air.  Philip  P.  Sharpies. 

FIG.  119.     "Rapid"  Mixers. 

A  fourth  method  of  utilizing  concrete  mixers  is  to  use  a  rotary 
dryer,  as  a  part  of  the  plant,  for  drying  the  aggregate. 

Dryers,  Storage  Bins,  and  Mixers.  In  several  types  of  plants 
the  aggregate  is  heated  in  rotary  dryers  from  which  the  dried 
material  is  transported  by  elevators  to  storage  bins.  In  some 
cases  the  aggregate  is  raised  to  the  storage  bins  before  being 
dried.  As  required,  the  aggregate  falls  by  gravity  into  the  mixer. 
The  heat  for  the  dryers  and  the  mixer  is  obtained  by  direct 
heat  from  fire-boxes  or  by  oil-burning  apparatus. 

Dryers,  Storage  Bins,  Weighing  Devices,  and  Mixers.  In  a 
complete  plant,  see  Figs.  120  and  121,  for  the  manufacture  of 
bituminous  concrete,  the  aggregate  is  carried  by  bucket-elevators 
to  rotary  dryers,  where  it  is  dried  and  the  dust  exhausted;  from 


FIG.  121.     Warren  Brothers'  Mixing  Plant. 


FIG.  122.     Weighing  Device  and  Pug  Mill  Mixer,  Warren  Brothers'  Mixing 

Plant. 


BITUMINOUS   CONCRETE  PAVEMENTS 


293 


the  dryer  the  aggregate  is  raised  to  the  storage  bins  by  elevators; 
when  required  the  aggregate  is  drawn  from  the  bins  to  a  weighing 
device,  see  Fig.  122,  and  from  there  deposited  into  a  mixer. 

COST  DATA.  The  cost  of  bituminous  concrete  pavements 
varies  with  the  kind  and  quantity  of  bituminous  material  used, 
the  character  of  the  aggregate  and  the  method  of  construction 
employed.  Using  an  aggregate  of  stone  varying  from  y$>  to  i^ 
inches  in  longest  dimensions,  mixed  with  1.5  gallons  of  bitumi- 
nous material  per  square  yard,  and  with  a  flush  coat  of  ^  gallon 
per  square  yard,  the  cost  of  a  2-inch  wearing  course  would  be 
about  30  to  50  cents  per  square  yard  in  excess  of  water-bound 
broken  stone  roads.  The  cost  of  pavements  of  Classes  i.  B. 
and  i.  C.  varies  from  $1.25  to  $2.25  per  square  yard,  including 
foundations  and  light  grading.  In  the  following  tables  are  given, 
for  several  localities  throughout  America,  the  average  1914  prices 
of  bituminous  concrete  pavements  and  foundations. 

Topeka  Bituminous  Concrete  Pavements. 

From  Engineering  and  Contracting,  April  7,   1915 


Price* 

Guar- 

Wearing 

Concrete 

Foundation 

City 

Square 
Yards 

per 
Sq.  Yd. 

antee, 
Years 

Course 
Thickness, 
Inches 

Thickness 
Inches 

Propor- 
tions 

Pittsfield,  Mass  
Trenton,  N.  J  
Minneapolis,  Minn.  . 
Des  Moines,  la  
Greenville  Tex 

30,567 
50,183 
42,622 
5,965 

30  ooo 

$1-94 

i-47 
1-75 
i-92t 
i   sot 

5 
•5 

5 
5 

3 

2 

2 

3 

2 

5 
5 
5 
5 
i 

I      3:6 
I     3  :6 
i     3:6 
I     3:6 

T        ^ 

*  Price  covers  pavement,  foundation,  and  shaping  subgrade. 
t  Does  not  include  shaping  subgrade. 

Bitulithic  Pavements. 

From  Engineering  and  Contracting,  April  7,   1915 


City 

Square 
Yards 

Price* 
per 
Sq.  Yd. 

Guar- 
antee, 
Years 

Wearing 
Course 
Thickness, 
Inches 

Concrete  Foundation 

Thickness 
Inches 

Propor- 
tions 

Boston,  Mass  
Providence,  R.  I  .... 
Utica,  N.  Y  
Asheville,  N.  C  
New  Orleans,  La  .... 
Butte  Mont 

54,842 

77,495 
30,496 
45,400 
14,370 
21,761 
47,629 

$2.75 
2.26 
2.26 
2.  10 
2.40 
2.85 

i-55t 

5 
5 
5 
5 
5 
5 

10 

2 
2 

3 
2 
2 
2 

2 

6 

5 
6 

5 
6 

5 
5 

13:7 
i      3     :6 
i      3t  :7 
i      2^  :  5 
i      3     :6 
13:5 
I3--7 

Toronto,  Quebec  .... 

*  Price  covers  pavement,  foundation,  and  shaping  subgrade. 
t  Does  not  include  shaping  subgrade. 


294 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


Asphalt  Block  Pavements. 

From  Engineering  and  Contracting,  April  7,  1915 


Prir^* 

Concrete 

Foundation 

City 

Square 
Yards 

per 
Sq.  Yd. 

antee, 
Years 

Thickness, 
Inches 

Propor- 
tions 

Holyoke,  Mass  

5,567 

$2.38 

4 

i     2^  :  5 

Jamestown,  N.  Y  
Niagara  Falls,  N.  Y  
Toledo  O 

9423 
34,165 
7,704. 

2-35t 
2.62 

2.00f 

i 

5 
6 

5 

i     2^  :s 
i     3       :6 
i      VA  :  6 

Windsor,  Ont  
Regina,  Sask  

36,086 

28,525 

2-75t 
3.00 

5 

15 

6 

5 

12       :4 
i     6 

*  Price  covers  pavement,  foundation,  and  shaping  subgrade. 
t  Does  not  include  shaping  subgrade. 


MAINTENANCE 

The  maintenance  of  bituminous  concrete  pavements  is  ac- 
complished in  a  manner  similar  to  that  described  in  the  chapter 
on  Bituminous  Macadam  Pavements.  (See  Fig.  123.) 

CHARACTERISTICS 

ADVANTAGES.  All  of  the  advantages  resulting  from  the  con- 
struction of  bituminous  surfaces  on  macadam  and  gravel  roads 


Courtesy  of  Mr.  Philip  P.  Sharpies 

FIG.  123.     Repairing  a  Trench  Opening  in  a  Bituminous  Concrete  Pavement. 


BITUMINOUS   CONCRETE   PAVEMENTS  295 

and  of  bituminous  macadam  pavements  may  be  cited  verbatim 
with  reference  to  bituminous  concrete  pavements.  Bituminous 
concrete  pavements  are  usually  more  stable  and  durable  than 
other  types  of  bituminous  pavements.  By  the  use  of  modern 
mixing  plants,  it  is  practicable  to  lay  certain  types  of  bitu- 


FIG.  124.     Result  of  Using  a  Poor  Grade  of  Tar. 

minous  concrete  pavements  of  Class  i.  A.  as  economically 
as  it  is  possible  ordinarily  to  build  bituminous  macadam 
pavements. 

DISADVANTAGES.  Slipperiness  with  seal  coats  of  some  bitu- 
minous materials  may  occur  and  thus  prove  a  disadvantage. 
It  is  evident  that  skilled  supervision  is  required,  which  may  be 
difficult  to  secure. 

CAUSES  OF  FAILURE.  It  should  be  noted  that  the  percentage 
of  failures  of  bituminous  concrete  pavements  is  much  smaller 
than  in  the  case  of  bituminous  macadam  pavements.  Failures 
may  be  considered  from  the  standpoint  of  the  materials  em- 
ployed and  methods  of  construction  adopted.  Failures  have 


296 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


occurred  because  the  type  of  pavement  used  was  not  suitable 
for  the  traffic  or  other  local  conditions. 

Materials.  Poor  and  unsuitable  materials  have  been  account- 
able for  certain  failures.  In  some  cases  an  apparent  cause  of 
failure  has  been  an  excess  of  flux  or  of  the  volatile  constituents 


FIG.  125.     Soft  Seal  Coat  Torn  up  Due  to  Adhesion  to  Tires. 


in  asphalt  cements.  Pavements  constructed  with  such  materi- 
als are  frequently  wavy,  due  to  the  movement  of  the  sur- 
face under  heavy  traffic.  Many  of  the  above  causes  of  failure 
would  be  eliminated  if  engineers  would  devote  more  time  to  a 
consideration  of  the  physical  and  chemical  properties  of  the 
materials  which  they  employ.  (See  Figs.  124  and  125.)  If  a 
bituminous  material  laboratory  is  not  connected  with  the  de- 
partment, it  should  be  neither  expensive  nor  difficult  to  se- 
cure certified  analyses  made  by  reputable  chemical  engineers. 

Either  too  large  broken  stone  or  stone  of  too  uniform  size 
may  cause  a  failure.  Especially  is  this  the  case  with  very  hard 
and  tough  broken  stone.  The  rocking  of  the  stone  causes  the 
formation  of  fine  cracks  which  eventually  lead  to  disintegration. 
Poor  combinations  of  sizes  of  broken  stone  and  sand  have  re- 


BITUMINOUS   CONCRETE   PAVEMENTS  297 

suited  in  segregation  during  mixing,  transportation,  or  spreading, 
resulting  in  a  pavement  of  varying  density  and  stability. 

Construction.  Many  cases  are  reported  where  materials  have 
been  overheated  due  to  the  belief  that  all  materials  may  be 
and  even  should  be  heated  to  the  same  temperature  before 
using  and  that  it  is  impossible  to  injure  bituminous  mate- 
rials by  heating  to  high  temperatures.  Overheating  of  the 
mineral  aggregate  has  caused  burning  of  the  bituminous 
material  in  some  instances  or  the  formation  of  a  thin  film 
of  bituminous  material  over  the  broken  stone  which  is  not  of 
sufficient  amount  to  bind  the  adjacent  stones  together.  The 
use  of  a  wet  aggregate  will  result  in  a  poor  mix  with  conse- 
quent unsatisfactory  results.  In  many  instances  the  seal  coat 
has  not  been  applied  uniformly.  The  result  is  either  uneco- 
nomical, due  to  the  necessity  of  a  second  application  before  75 
per  cent  of  the  surface  requires  retreatment,  or  the  disintegration 
of  the  pavement  whenever  bare  spots  occur  in  pavements  where 
a  coarse  aggregate  was  used  and  where  there  is  considerable 
horse-drawn  vehicle  traffic.  Some  failures  have  been  caused  by 
using  with  unheated  stone  bituminous  cements  which  will  not 
adhere  satisfactorily  or  which  mix  only  with  great  difficulty  under 
such  conditions.  Many  failures  are  due  to  poor  foundations. 

Careful  consideration  of  the  causes  of  failures  will  result  in 
material  benefit,  inasmuch  as  a  comprehensive  knowledge  of  the 
various  causes  of  failure  is  one  of  the  most  valuable  assets  of 
engineers  having  in  charge  the  construction  and  maintenance  of 
bituminous  surfaces  and  bituminous  pavements. 


CHAPTER  XIII 
SHEET  ASPHALT  AND  ROCK  ASPHALT  PAVEMENTS 

"  Sheet  asphalt  pavements  are  those  having  a  wearing  course 
composed  of  asphalt  cement  and  sand  of  predetermined  grading, 
with  or  without  the  addition  of  fine  material,  incorporated  to- 
gether by  mixing  methods."4  The  wearing  course  is  usually  laid 
upon  a  binder  course  of  bituminous  concrete  which  in  the  case 
of  first-class  pavements  has  been  laid  upon  a  cement-concrete 


FIG.    126.     Section   Showing   Construction   of   Sheet  Asphalt  Pavement    in 

Pittsburg,  Pa. 

foundation.  The  component  parts  of  a  sheet  asphalt  pavement 
are  clearly  shown  in  Fig.  126.  In  some  cases  the  binder  course 
is  omitted. 

"  Rock  asphalt  pavements  are  those  having  a  wearing  course 
composed  of  broken  or  pulverized  rock  asphalt  with  or  without 
the  addition  of  other  bituminous  materials."*  A  rock  asphalt 
pavement  composed  of  pulverized  rock  asphalt  has  the  same 
appearance  as  a  sheet  asphalt  pavement. 

DEVELOPMENT.  The  first  extensive  use  of  pulverized  rock 
asphalt  for  paving  streets  was  in  Paris  in  1854,  although  there 
are  records  of  its  use  for  this  purpose  as  early  as  1838.  From 
1854  to  1867  a  considerable  yardage  of  this  kind  of  pavement 
was  constructed,  but  it  was  not  until  1867  that  it  was  used  on 

*  Dec.,  1914  Proceedings,  Am.  Soc.  C.  E.,  pages  3017-3018. 
298 


SHEET  ASPHALT  AND  ROCK  ASPHALT        299 

a  large  scale.  The  rock  asphalt  used  in  the  first  pavements 
was  known  as  Val  de  Travers.  Later,  another  rock  asphalt 
known  as  Seyssel  rock  was  used  with  equal  success.  The  first 
asphalt  pavement  in  London  was  constructed  in  1869,  a  Val 
de  Travers  asphalt  rock  being  used.  By  the  close  of  1873  tne 
total  square  yards  paved  with  rock  asphalt  was  about  61,000. 
The  success  of  these  early  pavements  led  to  the  trial  of  this 
material  in  America.  The  excessive  cost  of  importing  the  mate- 
rial from  Europe  led  to  the  development  of  the  modern  sheet 
asphalt  pavement.  The  first  experiment  with  this  type  of 
asphalt  pavement  was  tried  out  in  Newark,  N.  J.,  in  1870.  In 
1876  Pennsylvania  Avenue,  Washington,  D.  C.,  was  surfaced 
with  this  material.  This  was  the  first  real  test  on  a  large  scale 
of  the  sheet  asphalt  pavement.  Until  1882,  however,  only  a 
few  cities  laid  sheet  asphalt,  but  from  that  time  its  use  has 
increased  so  rapidly  that  it  is  now  one  of  the  most  widely  used 
and  popular  kinds  of  pavement.  Although  there  are  several 
rock  asphalt  deposits  within  the  borders  of  the  United  States, 
some  of  which  would  make  a  good  pavement  similar  to  those 
constructed  in  Europe,  this  material  has  never  been  used  to 
any  great  extent.  The  freight  charges  in  most  instances  would 
make  the  cost  much  more  than  that  of  the  artificial  mixture. 

MATERIALS  FOR  SHEET   ASPHALT  PAVEMENTS 

ASPHALT  CEMENT.  The  bituminous  material  which  is  used 
in  the  construction  of  sheet  asphalt  pavements  is  known  as 
asphalt  cement.  In  the  trade  it  is  commonly  called  A.  C.  The 
asphalt  cements  used  in  the  United  States  and  Canada  are 
described  by  the  following  definition: 

"Asphalt  Cement.*  A  fluxed  or  unfluxed  asphaltic material, 
especially  prepared  as  to  quality  and  consistency,  suitable  for 
direct  use  in  the  manufacture  of  asphaltic  pavements,  and  having 
a  penetration  of  between  5  and  250." 

In  order  to  have  a  clear  idea  of  the  meaning  of  this  term, 
the  interrelationship  of  the  terms  covered  by  the  following 
definitions  should  be  considered. 

*  Dec.,  1914  Proceedings,  Am.  Soc.  C.  E.,  pages  3011  to  3015. 


300  ELEMENTS   OF   HIGHWAY   ENGINEERING 

"  Asphalt.*  f  Solid  or  semi-solid  native  bitumens,  solid  or 
semi-solid  bitumens  obtained  by  refining  petroleums,  or  solid 
or  semi-solid  bitumens  which  are  combinations  of  the  bitumens 
mentioned,  with  petroleums  or  derivatives  thereof,  which  melt 
on  the  application  of  heat,  and  which  consist  of  a  mixture  of 
hydrocarbons  and  their  derivatives  of  complex  structure,  largely 
cyclic  and  bridge  compounds." 

"  Bitumens*  f  are  mixtures  of  native  or  pyrogenous  hydro- 
carbons and  their  non-metallic  derivatives,  which  may  be  gases, 
liquids,  viscous  liquids,  or  solids,  and  which  are  soluble  in  carbon 
disulphide." 

"Flux.*f  Bitumens,  generally  liquid,  used  in  combination 
with  harder  bitumens  for  the  purpose  of  softening  the  latter." 

Many  specifications  for  sheet-asphalt  pavements  have  in- 
cluded clauses  covering  the  chemical  and  physical  properties 
of  refined  asphalt  (R.  A.),  flux,  and  asphalt  cement.  Further- 
more, some  specifications  have  covered  the  method  by  which 
the  refined  asphalt  and  flux  should  be  combined  in  order  to 
form  the  asphalt  cement.  There  is  a  marked  tendency  among 
engineers  and  chemists  to  place  emphasis  upon  the  specification 
for  the  asphalt  cement  and  omit  specifications  for  the  refined 
asphalt  and  the  flux.  This  practice  is  based  on  the  belief  that 
comprehensive  and  suitable  specifications  covering  the  physical 
and  chemical  properties  of  the  asphalt  cement  are  sufficient, 
as  the  "A.  C."  is  the  bituminous  material  which  is  used  in 
the  pavement. 

BINDER  STONE.  The  following  description  of  binder  stone 
used  in  the  construction  of  the  binder  course  is  typical  of  Ameri- 
can practice.  The  broken  stone  for  the  binder  course  should 
be  clean,  hard,  rough  surfaced,  and  sharp  angled,  of  compact 
surface  and  uniform  grain.  It  should  be  subjected  to  abrasion 
tests  and  toughness  tests  by  the  engineer  in  accordance  with 
methods  adopted  by  the  American  Society  for  Testing  Materials, 
August  15,  1908.  It  should  show  a  "French  coefficient  of  wear" 
of  not  less  than  7.0;  its  toughness  shall  be  not  less  than  6.0. 

*  Dec.,  1914  Proceedings,  Am.  Soc.  C.  E.,  pages  3011  to  3015. 

t  Proposed  by  Committee  D-4,  American  Society  for  Testing  Materials. 


SHEET  ASPHALT  AND   ROCK  ASPHALT 


301 


It  should  all  pass  a  screen  with  iJ4-inch  circular  openings, 
and  not  over  15  per  cent  shall  exceed  i^  inches  in  largest 
dimension.  No  fragments  should  exceed  2  inches  in  largest 
dimension.  The  stone  might  be  so  graded  as  to  show  the 
following  mesh  composition: 


Passing  10  mesh, 

15  to  35  percent. 
Passing  W  screen  and  retained  on 

10  mesh,  10  to  35  percent, 

Passing  i"  and  retained  on  j^j"  screen, 

20  to  60  percent. 
Passing  l%"  and  retained  on  i" 

screen,  15  to  55  percent. 


Total  passing  yZ" 

screen,  25  to  50 

percent. 

Total  passing  i  W 
and  retained  on 
W  screen,  50 
to  75  percent. 


Total  passing 
i"  screen,  45 
to  85  percent. 


If  the  stone  does  not  contain  the  proper  amount  of  material 
passing  the  j/2-inch,  the  deficiency  may  be  made  up  by  the 
addition  of  sand  so  that  the  resulting  mixture  will  conform 
with  the  above  requirements. 

The  above  limits  as  to  mesh  compositions  are  intended  to 
provide  for  such  permissible  variations  as  may  be  rendered 
necessary  by  the  available  sources  of  supply  and  the  character 
of  the  work  to  be  done.  The  mesh  composition  and  character 
of  the  stone  may  be  varied,  within  the  limits  above  specified, 
depending  upon  the  kind  of  asphalt  used  and  the  traffic  con- 
ditions upon  the  street  or  streets  to  be  paved. 

SAND  AND  FILLER  FOR  WEARING  SURFACE.  The  following 
description  of  sand  and  filler  may  be  considered  typical  for  the 
materials  of  a  wearing  course  to  be  subjected  to  medium  traffic. 
The  sand  should  be  clean,  hard  grained,  and  moderately  sharp. 
The  product  used  may  be  of  one  grade  or  a  mixture  of  two  or 
more  grades,  but  should  show  the  following  mesh  composition: 


Passing  200  mesh  o  to    5% 

Passing  100  mesh  and  retained  on  200  mesh  14  to  25% 
Passing  80  mesh  and  retained  on  100  mesh  6  to  21% 
Passing  50  mesh  and  retained  on  80  mesh  15  to  30% 
Passing  40  mesh  an  retained  on  50  mesh  10  to  25% 
Passing  30  mesh  and  retained  on  40  mesh  8  to  20% 
Passing  20  mesh  and  retained  on  30  mesh  5  to  15% 
Passing  10  mesh  and  retained  on  20  mesh  2  to  15% 


25  to  35% 
40  to  50% 

20  tO  30% 


The  mineral  filler  should  be  thoroughly  dry  limestone  dust, 
Dolomite  dust,  or  Portland  cement.     It  should  all  pass  a  30- 


302  ELEMENTS   OF   HIGHWAY   ENGINEERING 

mesh  per  linear  inch  sieve,  and  at  least  66  percent  should  pass 
a  2oo-mesh  per  linear  inch  sieve. 

CONSTRUCTION 

SHEET  ASPHALT  PAVEMENTS.  Subgrade  and  Foundation.  It 
is  essential  that  the  foundation  for  sheet  asphalt  should  be  firm 
and  unyielding  since  the  weight  of  traffic  must  be  carried  by  it.  A 
i  :  2  :  5  to  i  :  3  :  7  cement-concrete  is  used,  being  4  to  8  inches 
in  thickness,  depending  upon  the  amount  of  traffic  and  subsoil 
conditions.  The  concrete  must  be  thoroughly  set  before  the 
binder  course  is  laid.  Bituminous  concrete  has  been  used  in  a 
number  of  instances,  in  which  cases  the  binder  course  is  not 
needed.  This  type  of  foundation  is  not  advised,  since  the  bond 
between  it  and  the  wearing  course  is  so  firm  that  the  latter 
can  only  be  removed  with  difficulty  when  repairs  are  necessary, 
and,  furthermore,  the  foundation  is  not  sufficiently  stable  in 
most  instances  where  sheet  asphalt  is  economically  employed. 
A  4-inch  to  6-inch  broken  stone  road  coated  with  asphalt  or 
coal  tar  has  been  used.  This  practice  should  not  be  followed. 

Binder  Course.  Upon  the  foundation  the  binder  course  is 
laid  so  as  to  be  i  to  i^  inches  thick  after  rolling,  about  40  per 
cent  being  allowed  for  compression.  This  course  is  usually 
composed  of  broken  stone,  sand,  and  asphalt  cement  or  broken 
stone  and  asphalt  cement.  The  material  is  brought  on  to  the 
street  in  covered  dump  wagons,  at  200°  to  325°  F.,  depending 
upon  the  type  of  asphalt  cement  used,  deposited,  and  smoothed 
down  with  hot  shovels  and  rakes.  It  is  then  compacted  with 
a  tandem-roller.  Although  5-  to  8-ton  rollers  are  used,  more 
satisfactory  compaction  is  secured  by  employing  10-  to  1 2-ton 
tandem-rollers. 

Wearing  Course.  The  aggregate  consists  of  a  finely  graded 
sand  and  fine  filler  such  as  stone  dust  or  Portland  cement. 
Volcanic  dust  has  also  been  used  as  a  filler  with  satisfactory 
results.  The  wearing  course,  consisting  of  the  aggregate  and 
the  asphalt  cement,  is  usually  i>£  to  2  inches  in  depth  after 
rolling.  The  amount  of  bitumen  used  varies  from  9  to  13  per- 


SHEET  ASPHALT  AND  ROCK  ASPHALT         303 

cent.  It  is  brought  on  to  the  street  at  280°  to  325°  F.,  depending 
upon  the  type  of  asphalt  cement  used,  dumped,  and  spread  on  the 
binder  surface,  and  then  tamped  around  all  manholes,  gutters, 
and  curbs,  and  rolled  with  a  tandem-roller  weighing  5  to  10 
tons.  A  continued  rolling  is  very  essential,  as  a  constant  knead- 
ing action  is  necessary  to  secure  a  well-compacted  surface. 
Special  care  must  be  taken  along  street-car  rails  to  secure 
thorough  compaction.  Usually  one  to  three  courses  of  stone 
block  or  brick  are  laid  next  the  rail.  Eighteen  to  24  inches 
adjoining  the  curb  are  often  painted  with  hot  asphalt  cement 
to  secure  imperviousness  to  water. 

Asphalt  Plants.  A  complete  plant  includes  a  cold-sand  ele- 
vator, a  dryer,  a  hot-sand  elevator,  a  hot-sand  storage  bin  with 
screen,  an  asphalt  elevator,  a  flux  tank,  melting  tanks,  draw-off 
tanks,  a  sand-measuring  box,  a  dust  elevator,  bin  and  measuring 
box,  an  asphalt  cement  bucket,  and  a  mixer.  In  large  plants 
agitation  in  the  melting  tanks  is  necessary  in  order  to  prevent 
burning,  especially  when  the  asphalt  cement  is  heated  by  direct 
fire.  Agitation  may  be  accomplished  by  blowing  air  or  super- 
heated steam  through  the  asphalt  cement,  or  by  mechanical 
means.  In  the  case  of  asphalt  cements  containing  considerable 
foreign  material,  it  is  advisable  to  use  mechanical  agitation  or 
a  combination  of  mechanical  agitation  and  the  injection  of  air 
or  superheated  steam  in  order  to  prevent  the  impurities  from 
settling  to  the  bottom  of  the  melting  tanks.  The  mixing  device 
of  this  type  of  plant  consists  of  a  semi- cylindrical  trough  for 
holding  the  materials  to  be  mixed  together.  A  series  of  paddle 
wheels  revolves  on  a  horizontal  axle  which  is  fixed  at  either 
end  within  the  trough.  These  paddles  agitate  the  ingredients 
and  thus  produce  the  mix.  The  parts  are  all  suitably  arranged 
so  that  the  operations  follow  one  another  in  such  a  manner 
that  none  of  the  ingredients  of  the  mixture  have  to  be  handled 
by  hand  from  the  time  they  are  placed  in  the  receiving  end  of 
the  machine  until  they  leave  the  outlet  end.  (See  Fig.  127.) 

ROCK  ASPHALT  PAVEMENTS.  European  Practice.  In  Europe 
practically  all  of  the  asphalt  pavements  are  constructed  with  a 
wearing  course  of  pulverized  rock  asphalt.  The  naturally 


SHEET  ASPHALT  AND   ROCK  ASPHALT  305 

impregnated  rock  is  obtained  from  the  Val  de  Travers,  Seyssel, 
Vorwohle,  Limmer,  or  Ragusa  mines.  The  methoci  of  construc- 
tion employed  in  Europe  is  as  follows:  After  the  rock  asphalt 
is  pulverized,  the  powder  is  placed  in  slow,  revolving  cylinders 
and  subjected  to  a  heat  of  from  250°  to  280°  F.,  the  object 
being  to  drive  off  the  moisture.  This  powder  is  spread  on  a 
foundation  to  a  depth  of  2  inches  or  3  inches,  raked  even,  and 
tamped  with  hot  rams  or  tampers  weighing  about  twelve 
pounds,  and  finally  rolled  with  a  lo-ton  roller. 

American  Practice.  Borough  of  Manhattan.  The  1912  speci- 
fications of  the  Borough  of  Manhattan,  New  York  City,  allowed 
the  use  of  rock  asphalt  under  the  conditions  here  cited. 

"Should  any  of  the  rock  asphalts  be  used,  the  material  shall 
be  a  natural  bituminous  limestone  or  sandstone,  or  a  mixture 
of  the  two,  and  shall  be  prepared  and  laid  in  the  following 
manner:  The  lumps  of  rock,  after  being  mixed  in  the  proper 
proportions,  shall  be  finely  crushed  and  pulverized,  and  the 
powder  passed  through  a  2o-mesh  sieve.  In  case  of  the  use  of 
any  asphaltic  limestone,  or  of  a  mixture  of  an  asphaltic  lime- 
stone and  an  asphaltic  sandstone,  nothing  whatever  shall  be 
added  to  or  taken  from  the  powder  obtained  by  grinding  the 
natural  bituminous  rock.  The  rock  shall  contain  from  9  to 
12  percent  of  natural  bitumen.  This  powder  shall  be  heated 
in  a  suitable  apparatus  to  200°  or  250°  F.,  and  must  be  brought 
to  the  ground  at  a  temperature  of  not  less  than  180°  F.  in  carts 
made  for  the  purpose,  and  carefully  spread,  as  specified  for 
refined  asphalt  pavement,  to  such  a  depth  that  after  having 
received  its  ultimate  compression  it  will  have  a  thickness  of 
2^2  -inches  when  laid  on  concrete.  When  the  foundation  is 
other  than  concrete  it  shall  be  laid  on  a  i-inch  binder  course, 
as  heretofore  described,  and  the  net  thickness  of  the  rock  asphalt 
wearing  surface  after  compression  shall  be  2  inches.  The  surface 
shall  be  rendered  perfectly  even  by  tamping,  smoothing,  and 
rolling  with  heated  appliances  of  approved  design." 

Broken  Rock  Asphalt.  Rock  asphalt  is  sometimes  employed 
in  the  United  States  in  the  same  manner  as  broken  stone  is 
used.  One  method  of  construction  is  to  lay  on  the  foundation 


306 


ELEMENTS   OF  HIGHWAY   ENGINEERING 


course  of  broken  stone  a  2^2 -inch  course  of  i-inch  to  2-inch 
stone  and  roll  just  enough  to  render  firm.  Broken  rock  asphalt, 
containing  7  to  10  percent  bitumen,  is  then  raked  on  from 
dumping  boards  to  a  depth  of  >£  inch  and  rolled  in,  and  finally 
a  second  course  i  inch  deep  is  laid  and  rolled;  or  the  whole 
may  be  laid  in  one  course  1^2  inches  thick.  Old  macadam 
roads  may  be  resurfaced  by  first  scarifying  and  then  applying 
a  course  of  crushed  rock  asphalt  as  in  new  construction. 

COST  DATA.  The  average  cost  of  sheet  asphalt  pavements 
on  cement-concrete  foundation  varies  from  $1.50  to  §2.25  per 
square  yard.  In  the  following  table  are  given,  for  several  locali- 
ties throughout  America,  the  average  1914  prices  of  sheet 
asphalt  pavements  and  foundations  constructed  with  various 
thicknesses  of  wearing  courses,  binder  courses,  and  cement- 
concrete  foundations. 

From  Engineering  and  Contracting,  April  7,   1915 


Wear- 

Concrete 

City 

Square 
Yards 

Price* 
per 
Square 
Yard 

Guar- 
antee, 
Years 

ing 
Course 
Thick- 
ness, 
Inches 

Binder 
Course 
Thick- 
ness, 
Inches 

Foundation 

Thick- 
ness, 
Inches 

Propor- 
tions 

Boston,  Mass  

27,423 

$3-oo 

5 

\y 

ll/2 

6 

I      3  •'  7 

Brooklyn,  N.  Y  
Atlantic  City,  X.  J.  .  . 

680,877 
150,572 

•76 

•75 

5 

5 

2 

\/2 

6 

I      3:6 
i     3  :6 

Philadelphia,  Pa  

314,778 

91 

5 

2 

6 

i     3  :6 

Columbus,  O  

130,187 

2.  OOf 

5 

2 

6 

i     3:5 

Highland  Park,  Mich. 

45,485 

.62 

5 

\y2 

6 

3  :5 

Des  Moines,  la  

55,299 

92f 

5 

i/^j 

5 

3  :6 

Washington,  D.  C  .  .  . 

28,282 

.69t 

5 

\y2 

y* 

6 

3  =7 

Charlo  te,  N.  C  

40,OOO 

•54t 

5 

2 

4 

3  :6 

Lexington,  Ky  

29.9S5 

.90 

2 

6 

3  :  6 

Oakland,  Cal  

-7>  :7OO 

97,972 

.8of 

2 

6 

O 

3  :  6 

Portland,  Ore  

40,447 

•54t 

10 

2 

I 

5 

3:6 

*  Price  covers  pavement,  foundation,  and  preparation  of  subgrade. 
t  Does  not  include  preparation  of  subgrade. 


MAINTENANCE 

SHEET  ASPHALT  PAVEMENTS.  Failures  of  sheet  asphalt 
pavements  are  usually  due  either  to  defective  foundation,  dirt 
on  the  binder,  too  soft  asphalt  in  binder,  frost,  gas,  kerosene  or 
oil,  fires,  poor  construction,  or  lack  of  sufficient  traffic. 


SHEET  ASPHALT  AND  ROCK  ASPHALT         307 

Explanations  of  several  causes  of  deterioration  of  sheet 
asphalt  pavements  are  given  in  the  following  excdrpts.* 

"The  proper  maintenance  of  an  asphalt  pavement  involves 
the  making  of  such  repairs  to  it  from  time  to  time  as  are  neces- 
sary in  order  that  it  may  continue  to  render  efficient  service  as 
a  safe  and  smooth  roadway  or  street. 

"The  deterioration  which  eventually  renders  these  repairs 
necessary  commences  as  soon  as  the  pavement  is  laid  and  may 
be  broadly  classified  under  the  following  heads: 

"  i.  Defects  due  to  the  wear  and  tear  of  traffic. 

"2.  Defects  caused  by  the  deterioration,  through  age  and 
exposure,  of  the  bituminous  cementing  materials  used. 

"3.  Defects  in  construction. 

"  Traffic  Deterioration.  Under  traffic  the  surface  of  the  pave- 
ment is  abraded  and  gradually  wears  off  and  the  mineral  par- 
ticles exposed  on  the  top  are  more  or  less  crushed  and  broken. 
Under  heavy  traffic  and  unfavorable  weather  conditions,  these 
crushed  grains  become  active  centers  of  disintegration.  The 
crushed  particles  are  not  bound  together  by  the  asphalt  cement 
and  are  soon  swept  away.  The  holes  thus  made  in  the  pavement 
serve  to  retain  the  moisture  and  the  edges  of  the  holes  are 
eventually  more  or  less  broken  down,  thus  enlarging  the  hole. 
The  effect  of  this  action,  which  at  first  glance  appears  trivial, 
has  been  so  well  established  by  years  of  investigation  and  ex- 
perience that  it  has  become  axiomatic  in  the  paving  industry 
that  the  heavier  the  traffic  the  finer  must  be  the  particles  com- 
posing the  mineral  aggregate.  In  hot  weather  the  caulks  on 
horses'  shoes  sometimes  mark  up  the  pavement  to  a  very  con- 
siderable extent,  but  the  subsequent  action  of  vehicular  traffic 
wears  these  marks  out  almost  completely.  Nevertheless,  in  a 
community  unaccustomed  to  sheet  asphalt  pavements,  the  ap- 
pearance of  these  caulk  marks  in  a  new  pavement  is  always 
regarded  as  an  ominous  sign  presaging  its  speedy  destruction 
and  failure.  As  a  matter  of  fact,  if  the  pavement,  especially 

*  See  1912-1913  Lecture  by  Francis  P.  Smith  on  "Maintenance  of  Sheet 
Asphalt  Pavements,"  in  the  Graduate  Course  in  Highway  Engineering  at 
Columbia  University. 


308  ELEMENTS   OF   HIGHWAY   ENGINEERING 

when  newly  laid,  were  not  soft  enough  to  show  these  marks, 
it  would  be  an  almost  infallible  sign  that  the  asphalt  cement 
used  in  it  was  too  hard  and  that  the  total  life  of  the  pavement 
would  be  less  than  if  a  softer  asphalt  cement  had  been  used. 
Traffic  on  a  pavement  always  compresses  it  and  increases  its 
density,  and  for  this  reason  a  two-year-old  pavement  will  always 
mark  up  less  than  a  new  one.  The  pressure  per  square  inch 
exerted  by  the  comparatively  narrow  tire  of  a  heavily  loaded 
vehicle  is  much  greater  than  that  exerted  by  the  heaviest  steam- 
roller used  in  the  laying  of  sheet  asphalt  pavements.  Even  if 
this  were  not  the  case,  the  kneading  action  produced  by  narrow 
tires  passing  many  times  over  the  surface  would  always  give 
greater  compression  than  could  be  obtained  by  the  action  of 
the  broad  tires  of  a  steam-roller. 

"When  the  traffic  is  confined  to  a  comparatively  narrow 
space  and  is  always  in  the  same  direction,  a  distinct  pushing 
force  is  exerted  on  the  pavement.  Whenever  the  pavement 
lacks  inherent  stability,  due  to  an  improper  mineral  aggregate 
or  bitumen  which  is  lacking  in  cementing  value  from  natural 
causes  or  the  rotting  action  of  gas  or  water,  or  a  combination 
of  these  defects,  very  distinct  waves  or  bumps  will  be  produced 
by  the  action  of  heavy  traffic.  Investigation  will  almost  always 
show  defective  binder  in  these  spots,  or  too  soft  an  asphalt 
cement,  or  too  great  a  thickness  of  pavement  owing  to  an  error 
in  the  grade  of  the  concrete. 

"  Effect  of  Ageing  and  Exposure.  All  bituminous  materials 
used  in  paving  work  deteriorate  upon  exposure  to  the  elements 
and  to  the  rotting  action  of  escaping  gas,  water,  and  street 
liquids.  The  lighter  oils  contained  in  them  gradually  volatilize, 
thus  hardening  the  remaining  bitumen.  In  order  to  guard  against 
this  and  prolong  the  effective  life  of  the  pavement,  the  asphalt 
cement  used  in  its  construction  is  made  as  soft  as  possible 
without  rendering  the  pavement  too  mushy  when  new. 

"  Some  asphalts  are  more  easily  rotted  by  water  action  than 
are  others.  With  such  asphalts  it  is  more  than  ever  necessary 
to  make  the  pavement  as  dense  as  possible  to  prevent  the  water 
from  getting  into  it.  Generally  speaking,  with  all  asphalts  the 


SHEET  ASPHALT  AND  ROCK  ASPHALT         309 

wetter  the  climatic  or  other  conditions,  the  denser  and  richer 
in  bitumen  should  the  mixture  be  made.  Where  water  is  allowed 
to  remain  in  the  gutters,  the  rotting  will  frequently  be  very 
rapid  and  this  will  be  still  more  marked  if,  as  in  some  towns, 
the  dirty  wash-water  from  houses  is  discharged  into  the  gutters. 
Too  frequent  washing  of  a  pavement  with  water  at  a  high 
pressure  is  also  bad,  as  the  abrasive  action  of  such  a  jet  is  very 
considerable  and  acts  in  the  same  way  as  the  stream  from  a 
hydraulic  nozzle. 

"  Gas  leaks  produce  a  very  similar  result  and  the  gas  some- 
times travels  a  long  distance  from  the  point  of  leakage  before 
it  actually  comes  in  contact  with  the  pavement. 

"Another  cause  for  the  deterioration  of  sheet  asphalt  pave- 
ment is  lack  of  traffic.  Pavements  laid  on  outlying  residence 
streets  and  culs-de-sac  with  little  or  no  traffic  crack  much  more 
quickly  than  if  they  were  subjected  to  a  moderate  traffic,  which 
appears  to  be  necessary  to  keep  the  life  in  the  pavement.  This  is 
probably  due  to  the  fact  that  the  surface  is  not  in  such  cases  kept 
at  the  maximum  density  by  the  action  of  traffic  and  gradually 
becomes  porous,  thus  facilitating  the  evaporation  of  the  lighter 
oils,  and  also  to  the  fact  that  the  kneading  action  of  traffic, 
like  the  continual  use  of  a  rubber  band,  tends  to  keep  the  life, 
so  to  speak,  in  the  bitumen,  and  equalizes  the  stresses  set  up 
by  contraction  and  expansion. 

"Defects  in  Construction.  Unless  the  foundation  is  rigid 
and  of  sufficient  strength  to  carry  the  weight  of  the  traffic 
passing  over  the  finished  pavement,  no  sheet  asphalt  wearing 
surface  will  give  satisfactory  service.  (See  Fig.  128.)  Being 
plastic  at  all  normal  temperatures,  the  wearing  surface  will  not 
bridge  over  any  depressions  formed  by  the  sinking  or  failure  of 
the  foundation,  but  wifl  sink  with  it. 

"The  best  modern  practice  calls  for  the  use  of  the  tight 
binder,  as  it  gives  a  much  firmer  foundation  for  the  wearing 
surface  and  will  not  be  broken  up  and  loosened  from  the  con- 
crete by  the  passage  over  it  of  the  teams  hauling  the  hot  surface 
mixture.  Poor  binder  will  break  up  very  easily — sometimes  it 
can  be  kicked  up,  and  the  hauling  of  the  hot  surface  mixture 


310 


ELEMENTS   OF  HIGHWAY   ENGINEERING 


over  it  will  damage  it  very  seriously.  Surface  mixture  laid  on 
a  binder  of  this  kind  which  has  been  badly  broken  up  might 
almost  as  well  be  laid  on  loose  broken  stone  and  will  not  give 
satisfactory  service  under  heavy  traffic.  The  binder  should  of 
course  be  thoroughly  compressed  with  a  steam-roller  before 
laying  the  wearing  surface  on  it.  Lack  of  compression  will 


FIG.  128.     Crack  in  Concrete  Foundation  Due  to  Poorly  Drained  Subgrade. 

produce  an  unsatisfactory  foundation  for  the  wearing  surface, 
and,  as  previously  mentioned,  binder  which  is  too  cold  or  made 
with  too  hard  an  asphalt  cement  or  an  insufficient  quantity  of 
asphalt  cement  cannot  be  properly  compressed  into  a  dense, 
tough  mass.  Before  laying  the  surface  mixture  on  the  finished 
binder  course,  the  latter  should  be  dry  and  swept  clean  of  dirt; 
otherwise  the  layer  of  wearing  surface  will  not  adhere  properly 
to  it." 

Repairs  and  Conditions  of  Guarantee.  From  the  1914  speci- 
fications of  the  American  Society  of  Municipal  Improvements 
the  following  quotations  are  taken  which  cover  the  methods 
to  be  used  in  repairing  sheet  asphalt  pavements  and  the  con- 
dition of  the  pavement,  at  the  end  of  the  guarantee  period, 
which  should  be  insisted  upon. 


312 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


"Repairing.  Repairs,  except  as  provided  for  below,  shall  in 
all  cases  be  made  by  cutting  out  the  defective  binder  and  wearing 
surface  down  to  the  concrete  and  replacing  them  by  new  and 
freshly  prepared  binder  and  wearing  surface  made  and  laid  in 
strict  accordance  with  these  specifications. 

"Whenever  any  defects  are  caused  by  the  failure  of  the 
foundation,  the  pavement,  including  such  foundation,  shall  be 


FIG.  130.     Hand-drawn  Surface  Heater. 

taken  up  and  relaid  with  freshly  prepared  material  made  and 
laid  in  strict  accordance  with  these  specifications. 

"In  all  cases  the  surface  of  the  finished  repair  shall  be  at 
the  grade  of  the  adjoining  pavement  and  in  accordance  with  the 
contour  of  the  street. 

"The  surface-heater  method  of  repairing  may  be  used  only 
in  those  cases  where  the  repairs  are  not  rendered  necessary  by: 

(a)  Failure  of  concrete. 

(b)  Failure  of  the  binder. 

(c)  Failure  caused  by  the  disintegration  of  the  lower  portion 
of  the  wearing  surface. 

"Whenever  the  surface  heater,  see  Figs.  129  and  130,  method 
is  employed,  all  defective  surface  shall  be  removed  before  re- 
placing it  with  new  material.  In  all  cases  the  old  surface  shall  be 


SHEET  ASPHALT  AND  ROCK  ASPHALT         313 

removed  to  a  depth  of  not  less  than  %  inch  and  the  new  surface 
must,  when  compressed,  be  not  less  than  y2  inch  in  thickness. 
The  heat  shall  be  applied  in  such  a  manner  as  not  to  injure 
the  remaining  pavement.  All  burnt  and  loose  material  shall 
at  once  be  completely  removed  and,  while  the  remaining  portion 
of  the  old  pavement  is  still  warm,  shall  be  replaced  by  new 
and  freshly  prepared  wearing  surface  made  and  laid  in  strict 
accordance  with  these  specifications. 

"Conditions  at  Expiration  of  Guarantee.  In  addition  to  the 
proper  maintenance  of  the  pavement  during  the  period  of  guar- 
antee, the  contractor  shall,  at  his  own  expense,  just  before  the 
expiration  of  the  guarantee  period,  make  such  repairs  as  may 
be  necessary  to  produce  a  pavement  which  shall: 

"  (a)  Have  a  contour  substantially  conforming  to  that  of  the 
pavement  as  first  laid  and  free  from  depressions  of  any  kind 
exceeding  3/6  of  an  inch  in  depth  as  measured  between  any  two 
points  4  feet  apart  on  a  line  conforming  substantially  to  the 
original  contour  of  the  street. 

"  (b)  Be  free  from  cracks  or  depressions  showing  disintegra- 
tion of  the  surface  mixture. 

"  (c)   Contain  no  disintegrated  surface  mixture. 

"  (d)  Not  have  been  reduced  in  thickness  more  than  3/£  of 
an  inch  in  any  part. 

"  (e)  Have  a  foundation  free  from  such  cracks  or  defects  as 
\vill  cause  disintegration  or  settling  of  the  pavement  or  impair 
its  usefulness  as  a  roadway." 

CHARACTERISTICS 

SHEET  ASPHALT  PAVEMENT.  This  type  of  pavement,  when 
properly  constructed  on  a  cement-concrete  foundation,  is  durable 
under  heavy  traffic  such  as  is  characteristic  of  the  streets  of 
shopping  districts  in  large  municipalities.  It  is  very  low  in 
tractive  resistance,  easy  to  clean,  and  is  non-productive  of  dust 
from  abrasion  of  the  wearing  course.  It  is  usually  slippery  on 
grades  over  3  to  4  percent.  When  in  good  condition  very  little . 
noise  results  from  the  passage  of  the  wheels  of  vehicles,  but 


314  ELEMENTS   OF   HIGHWAY   ENGINEERING 

horses'  hoofs  striking  the  pavement  give  off  a  sharp  metallic 
noise. 

ROCK  ASPHALT  PAVEMENT.  The  European  pavements  con- 
structed of  pulverized  rock  asphalt  possess  the  characteristics 
of  sheet  asphalt  pavements  except  that  they  are  more  slippery. 


CHAPTER  XIV 
CEMENT-CONCRETE  PAVEMENTS 

DEVELOPMENT.  The  first  piece  of  cement-concrete  pave- 
ment was  laid  in  Inverness,  Scotland,  in  1865,  as  an  experimental 
section,  being  about  one  hundred  and  fifty  feet  long.  In  1866 
another  experiment  was  tried  in  Edinburgh.  Cement-concrete 
pavements  have  not  been  adopted  as  a  standard  type  in  Europe. 

The  first  cement-concrete  pavement  in  the  United  States 
was  laid  in  Belief ontaine,  Ohio,  in  1893.  It  was  not  until  1900, 
however,  that  this  material  was  used  to  any  great  extent.  The 
work  of  the  highway  department  of  Wayne  County,  Michigan, 
has  been  notable  from  the  standpoint  of  development  of  efficient 
methods  of  construction  and  maintenance.  At  the  close  of  1914 
the  county  had  constructed  over  100  miles  of  cement-concrete 
pavements.  During  1914  the  approximate  amount  laid  in  the 
United  States  comprised  about  seventeen  million  square  yards. 
During  the  past  few  years  it  has  been  demonstrated  that  the 
application  of  a  bituminous  surface  to  the  pavement  makes  it 
more  desirable.  The  construction  of  satisfactory  bituminous 
surfaces  on  this  class  of  pavement  is,  however,  very  difficult. 

THE  CEMENT-CONCRETE 

INGREDIENTS  AND  PROPORTIONING.  The  materials  used  for 
the  aggregate  of  a  cement-concrete  pavement  are  generally  sand 
and  either  broken  stone  or  gravel.  The  broken  stone  employed 
should  be  obtained  by  crushing  hard,  tough  rock.  Preferably 
the  stone  should  be  composed  of  naturally  graded  sizes  and 
free  from  dust  or  dirt.  Sometimes,  however,  the  run  of  the 
crusher  may  be  used,  including  the  dust,  which  is  acceptable 
provided  that  part  of  the  stone  below  ^  inch  in  size  is  reckoned 
as  fine  aggregate  in  making  up  the  proportions.  What  has  been 

315 


316  ELEMENTS   OF  HIGHWAY   ENGINEERING 

said  relative  to  broken  stone  applies  as  well  to  gravel,  since  a 
screened  gravel  with  the  fine  material  eliminated  allows  a  more 
accurate  determination  of  the  correct  proportions.  Some  engi- 
neers prefer  stone  and  others  gravel,  either  being  allowed  in 
some  specifications.  The  sand  used  should  be  clean,  sharp,  and 
coarse,  free  from  loam,  clay,  and  any  vegetable  or  organic  matter. 
The  cement  should  be  a  first-class  Portland  cement  that  will 
meet  the  standard  specifications  of  the  American  Society  of 
Civil  Engineers.  Care  should  be  taken  to  use  clean  water, 
since  water  which  contains  any  alkalies  or  acids  will  be  detri- 
mental to  the  concrete.  The  theory  of  the  correct  proportionirg 
of  concrete  has  been  briefly  stated  in  Chapter  V.  The  propor- 
tions which  were  given  in  connection  with  the  construction  of 
concrete  foundations  are  not  rich  enough  in  either  cement  or 
mortar  to  make  satisfactory  concrete  which  is  to  be  subjected 
to  the  abrasive  and  impact  forces  of  traffic.  The  proportions 
used  for  cement-concrete  pavements  vary  from  i  :  i^  '•  3  to 
1:3:6. 

CONSTRUCTION 

SUBGRADE  AND  FOUNDATION.  Cement-concrete  pavements 
should  be  laid  only  on  a  well-compacted  and  well-drained 
subgrade.  If  the  subgrade  is  of  clay,  it  should  be  replaced 
with  clinker,  broken  stone,  cinders,  gravel,  or  some  other 
suitable  material.  The  surface  should  usually  be  made 
flat  and  should  be  thoroughly  rolled  with  a  medium-weight 
roller.  Prior  to  the  deposition  of  concrete  the  subgrade  should 
be  thoroughly  wet,  otherwise  the  subgrade  will  absorb  water 
from  the  concrete,  thus  preventing  a  uniform  set  and  decreasing 
its  strength.  In  replacing  old  broken  stone  roads  with  a  cement- 
concrete  pavement,  it  is  possible  to  dig  up  the  broken  stone 
roadway,  screen  the  broken  stone,  and  use  it  as  the  aggregate 
in  the  concrete.  In  Chapter  V  the  subject  of  foundations  was 
considered  from  two  standpoints,  natural  and  artificial.  In  this 
connection  it  was  assumed  that  the  lower  course  of  a  broken 
stone  road  was  an  artificial  foundation  for  the  upper  course. 
A  similar  condition  exists  in  some  cement-concrete  pavements 


CEMENT-CONCRETE   PAVEMENTS  317 

which  are  built  in  two  courses,  the  upper  one  being  the  wearing 
course  and  the  lower  one  the  artificial  foundation. 

CONSTRUCTING  THE  PAVEMENT.  The  formulas  for  the 
amount  and  distribution  of  crown  are  given  in  Chapter  IV. 
Usually  the  average  transverse  slope  does  not  exceed  }/±  inch 
per  foot.  There  is  a  variety  of  methods  of  constructing  a 
cement-concrete  pavement.  Mixing  and  grouting  methods  are 
employed.  In  the  mixing  method  the  entire  thickness  of  the 
concrete  may  be  deposited  at  one  time  or  the  pavement  may 
be  constructed  in  two  courses.  In  the  grouting  method  the 
aggregate  is  laid,  rolled  in  place,  and  filled  with  a  cement 
grout.  In  a  few  instances,  steel  reinforcement  has  been  used  in 
pavements  built  by  both  the  mixing  and  the  grouting  methods. 
Another  type  of  construction  which  has  been  used  is  that  of 
molding  concrete  into  small  cubes  and  laying  the  same  as  a 
small  block  pavement.  The  practice  of  painting  the  concrete 
surface  with  a  coat  of  bituminous  material  has  given  good 
results  in  some  instances. 

Mixing  Methods.  In  cement-concrete  pavements  constructed 
by  the  mixing  method,  the  concrete  is  deposited  in  one  or  two 
layers.  Both  methods  have  been  tried  in  Wayne  County,  Michi- 
gan, the  construction  of  two-course  pavements  having  been 
abandoned.  It  is  evident  that  in  constructing  a  two-course 
pavement  there  will  be  a  plane  of  weakness  between  the  two 
courses.  Although  it  is  possible  in  the  two-course  method  to 
construct  the  top  with  a  richer  mix,  this  hardly  offsets  the  ad- 
vantages derived  from  having  the  entire  depth  of  concrete 
deposited  at  one  time. 

The  mixing  of  concrete  by  machine  has  been  considered  in 
Chapter  V.  In  the  construction  of  cement-concrete  pavements 
continuous  mixers  should  not  be  used  as  it  is  impracticable  to 
secure  uniform  results.  Under  average  conditions  the  best  re- 
sults are  secured  with  a  batch  mixer  to  which  is  attached  a 
boom  carrying  a  travelling  bucket.  Segregation  of  the  aggre- 
gate does  not  occur  to  any  marked  degree  when  this  type  of 
mixer  is  used.  The  mixing  machines  should  be  run  on  planks 
so  that  the  subgrade  will  not  be  disturbed.  The  general  rules 


318 


ELEMENTS   OF  HIGHWAY   ENGINEERING 


which  were  given  in  Chapter  V  relative  to  handling  the  mixed 
concrete  during  construction  and  its  treatment  after  being  laid 
apply  as  well  to  constructing  cement-concrete  pavements.  More 
attention  should  be  paid  to  obtaining  a  smooth  and  regular 
surface  in  constructing  cement-concrete  pavements  than  is  usu- 
ally accorded  concrete  foundations.  The  use  of  heavy  templates 


- 
- 

-A  v  <-'  '*.;v> 


••^•^•^•HMHMI 

Courtesy  of  the  Association  of  American  Portland  Cement  Manufacturers. 

FIG.  131.    Template  and  Bridge  Used  in  the  Construction  of  Cement-Concrete 

Pavements. 


to  strike  the  surface  of  the  concrete  and  of  bridges  which  span 
the  concrete  surface,  thus  enabling  the  laborers  to  work  over 
the  surface  without  standing  on  it,  should  be  insisted  upon. 
(See  Fig.  131.)  A  slightly  roughened  surface  maybe  obtained 
by  marking  the  concrete,  before  it  sets  hard,  with  a  grooving 
tool,  by  the  use  of  a  wood  float,  or  by  brooming  the  surface 
with  a  rather  stiff  broom.  It  is  also  important  to  protect  the 
surface  from  too  rapid  drying  out  while  the  concrete  is  curing, 
otherwise  shrinkage  cracks  are  liable  to  occur.  This  is  accom- 
plished sometimes  by  covering  the  pavement  as  soon  as  it  has 


CEMENT-CONCRETE   PAVEMENTS  319 

taken  its  initial  set  with  a  canvas  which  is  kept  moist  for  a  few 
hours.  The  canvas  is  then  removed  and  the  surface  is  covered 
with  a  layer  of  sand  or  earth  which  is  kept  thoroughly  moist  for 
a  period  of  two  weeks. 

One-Course  Method.  A  one-course  pavement  is  constructed 
in  Wayne  County,  Michigan,  'in  the  following  manner:  The 
concrete  is  mixed  in  the  proportions  of  i  :  i*4  :  3,  and  is  laid 
on  a  flat  subgrade  to  a  depth  of  6  inches  at  the  sides  and  8  inches 
in  the  center.  The  ingredients  are  machine  mixed  and  the 
concrete  is  placed  and  tamped  on  a  firmly  compacted  subgrade. 
The  surface  is  struck  off  with  a  plank  template  similar  to  the 
one  shown  in  Fig.  131.  Each  day's  work  is  finished  up  to  a 
transverse  expansion  joint,  such  joints  being  constructed  every 
25  feet  along  the  pavement. 

Two-Course  Method.  A  common  method  of  constructing  a 
two-course  pavement  may  be  described  as  follows:  A  layer  of 
concrete,  which  will  be  4  inches  thick  after  compaction,  is  placed 
on  the  previously  prepared  subgrade.  The  proportions  of  the 
ingredients  in  this  layer  are  variable,  but  a  mixture  of 
i  :  2^/2  :  5  may  be  considered  average  practice.  After  this 
layer  has  been  shaped  up  and  tamped,  and  before  it  has  begun 
to  set,  a  wearing  course,  2  inches  in  thickness,  is  constructed 
upon  it.  The  composition  of  the  wearing  course  is  also  quite 
variable.  It  may  consist  of  a  mixture  of  sand  and  cement  or 
it  may  be  composed  of  a  mixture  of  sand,  small-sized  crushed 
stone,  and  cement.  Cement  and  sand  mixed  in  the  proportions 
of  i  :  2  have  been  used.  Surface  mixtures  of  which  broken 
stone  formed  a  part  have  been  made  up  of  one  part  cement, 
one  part  sand,  and  one  part  of  %-  to  ^-inch  chips.  Other 
features  of  the  construction  do  not  differ  essentially  from  those 
described  under  one-course  methods. 

The  Blome  concrete  pavements  are  constructed  as  a  two- 
course  pavement,  the  lower  course  being  from  5  to  6  inches 
thick  and  the  wearing  surface  being  about  ij^"  inches  thick. 
The  wearing  surface  is  composed  of  one  part  cement  to  one  and 
one-half  parts  of  aggregate,  which  is  made  up  of  50  percent  of 
,  30  percent  of  ^-inch,  and  20  percent  of  / 


320  ELEMENTS   OF  HIGHWAY  ENGINEERING 

granite  screenings.  The  surface,  after  it  is  laid,  is  cut  into 
4//2-  by  Q-inch  blocks  by  special  grooving  tools,  the  grooves 
being  ^-inch  wide  and  ^-inch  deep. 

Reinforced  Pavements.  Reinforced  concrete  pavements  are 
usually  constructed  by  the  two-course  method.  The  reinforce- 
ment usually  consists  of  woven  wire  or  expanded  metal,  al- 
though a  mesh  work  of  small  round  bars  is  sometimes  used. 
The  reinforcement  is  universally  placed  between  the  base  and 
the  wearing  surface.  This  type  of  pavement  may  be  said  to 
be  in  an  experimental  stage.  In  practically  all  instances  where 
pavements  have  been  constructed  in  this  manner  both  longi- 
tudinal expansion  joints  at  the  curbs  and  transverse  expansion 
joints  across  the  pavement  have  been  built  at  intervals.  Some 
engineers  also  use  reinforcement  in  cement-concrete  pavements 
over  25  feet  in  width  instead  of  using  a  longitudinal  expansion 
joint  in  the  center. 

Oil  Cement-Concrete.  In  order  to  make  the  concrete  more 
waterproof,  and  at  the  same  time  to  enable  it  to  resist  the  changes 
of  temperature  more  effectively,  experimental  pavements  of  oil 
cement-concrete  have  been  built.  The  pavement  is  constructed 
in  the  same  manner  as  the  ordinary  concrete  pavements  built 
by  the  mixing  method,  except  that  a  fluid  residual  petroleum  is 
added  to  the  mix  in  an  amount  varying  from  10  to  18  percent 
of  the  weight  of  the  cement.  The  addition  of  oil  weakens  the 
strength  of  the  concrete,  although  it  makes  the  concrete  more 
impervious.  This  method  of  construction  has  not  shown  any 
advantages  which  would  warrant  its  adoption. 

Expansion  Joints.  Both  longitudinal  joints  along  the  curbs 
and  transverse  joints  should  be  provided.  There  will  be 
more  or  less  contraction  and  expansion  of  the  concrete  due 
to  changes  of  temperature,  variation  in  the  moisture  content  of 
concrete,  and  variation  in  the  condition  and  character  of  the 
subgrade.  If  expansion  joints  are  not  present,  when  the  con- 
crete contracts,  the  tensile  strength  of  the  concrete  will  be  ex- 
ceeded and  the  pavement  will  crack;  when  it  expands  it  will 
tend  to  crush,  spall,  or  bulge.  Fig.  132  shows  a  crack  in  a 
cement-concrete  pavement  due  to  contraction.  If  the  expansion 


CEMENT-CONCRETE   PAVEMENTS 


321 


produces  forces  that  are  in  excess  of  the  compre^sive  strength 
of  the  concrete,  the  concrete  will  crush  along  the  crack.  The 
edges  of  the  joints  must  be  protected  from  the  abrasive  action 
of  the  traffic,  and  it  is  obvious  that  the  joints  should  be  filled 
with  a  material  that  will  allow  some  movement  between  the 
joints  as  the  pavement  expands  and  contracts. 

The  width  of  the  longitudinal  joints  will  depend  somewhat 
upon  the  width  of  the  pavement.    They  are  usually  made  from 


FIG.  132.     Crack  in  Cement-Concrete  Pavement  Due  to  Contraction. 


j/2  to  ij/2  inches  wide  and  are  filled  with  a  bituminous  filler  or 
a  patented  expansion  joint  is  employed.  The  width  of  the 
transverse  joints  depends  upon  the  distance  between  them. 
It  is  considered  better  practice  to  construct  narrow  joints 
at  short  intervals  apart  rather  than  wide  ones  far  apart.  Trans- 
verse joints  are  placed  from  15  to  50  feet  apart,  25  feet  being 
an  average  distance. 

In  constructing  concrete  roads  in  Michigan  several  kinds  of 
transverse  expansion  joints  have  been  used.  The  joints  have 
been  filled  with  two  thicknesses  of  three-ply  tar  paper,  with 
^-inch  boards  of  southern  pine,  and  with  a  composition  of 
asphalt,  still  wax,  and  pitch.  To  protect  the  edges  of  the  joints, 


322 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


angle  irons  have  been  built  into  the  surface  of  the  road.    The 
use  of  angle  irons  proved  so  satisfactory  in  Wayne  County, 


FIG.    133.     Expansion-Contraction   Joint   in   Cement-Concrete   Pavement. 


FIG.  134.     Hassam  Cement  Grout  Mixer  and  Distributor. 

Michigan,  that  a  modified  form  of  angle  iron  was  developed 
which  was  used  in  all  of  the  1912  pavements  constructed  of 
concrete.  It  consists  of  two  soft  steel  plates,  >^-inch  thick  and 


CEMENT-CONCRETE   PAVEMENTS  323 

3  inches  wide,  which  are  clamped  to  a  dividing  board,  the  top 
edge  of  which  is  shaped  to  conform  to  the  crown  of  the  finished 
road.  The  plates  are  provided  with  means  to  tie  them  securely 
to  the  concrete  base  and  wearing  surface.  Between  the  plates 
are  placed  twro  thicknesses  of  three-ply  asphalted  cement  felt 
about  one-fourth  inch  thick  which  extends  the  entire  depth  of 
the  concrete.  (See  Fig.  133.) 

Grouting  Method.     Pavements  constructed  by  the  grouting 
method  are  generally  built  in  two  courses.     This  method  of 


FIG.  135.     Rolling  Hassam  Cement-Concrete  Pavement. 

construction  has  been  developed  by  the  Hassam  Paving 
Company.  A  layer  of  broken  stone  ranging  in  size  from  i%  to 
2^2  inches  is  placed  on  the  surface  and  rolled  to  a  thickness  of 
4  inches  so  that  the  top  will  be  2  inches  below  the  finished 
grade  of  the  pavement.  This  course  is  poured  with  a  grout 
composed  of  one  part  cement  and  three  parts  sand.  The  grout 
is  machine  mixed,  and  is  mechanically  agitated  during  the  proc- 
ess of  pouring,  so  that  there  is  never  any  segregation  of  the- 
cement  and  sand.  The  grout  mixers,  see  Fig.  134,  are  drawn 
along  the  roadway  and  the  grout  flows  from  the  machines, 
through  a  pipe  to  the  surface.  During  the  process  of  grouting, 
rolling  is  continued,  see  Fig.  135,  and  grout  is  poured  until  the. 


324 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


voids  in  the  stone  are  well  filled.  On  top  of  this  surface  a  wearing 
course  is  constructed  which  consists  of  a  2 -inch  layer  of  trap 
rock.  This  is  first  rolled  and  laid  in  a  similar  manner  to  that 
of  the  first  course,  except  that  a  thin  grout  composed  of  one 
part  of  cement  and  two  parts  of  sand  is  used.  The  pavement 
is  finished  off  by  brooming  and  brushing  into  the  surface  a 
thick  grout  composed  of  one  part  cement,  one  part  sand,  and 
one  part  pea-size  trap  rock.  The  pavement  is  thoroughly  rolled 


Courtesy  of  Wm.  PI.  Connell 


FIG.  136.     Section  of  Cement-Concrete  Pavement  Constructed  by  the  Grouting 

Method. 

until  the  voids  are  filled  in  each  instance  and  the  surface  has 
become  smooth.  Fig.  136  shows  a  section  cut  from  a  pave- 
ment constructed  by  this  method.  The  Long  Island  Motor 
Parkway  is  one  example  of  a  pavement  constructed  by  the 
Hassam  method,  except  that  in  this  case  woven  wire  reinforce- 
ment was  used  and  the  stone  was  laid  in  one  course.  The  total 
depth  of  this  pavement  is  5  inches,  and  2^  inches  from  the 
surface  is  placed  the  sheet  of  woven  wire  reinforcement  which 
extends  the  full  width  of  the  roadway. 

Bituminous  Surfaces  on  Concrete.     A  bituminous  surface 
constructed  on  the  surface  of  a  concrete  pavement  protects  the 


CEMENT-CONCRETE   PAVEMENTS 


325 


surface  of  the  concrete  from  abrasive  action  of  traffic,  offers 
a  better  foothold  with  certain  kinds  of  bituminous  materials, 
eliminates  the  dust  which  is  otherwise  liable  to  form  on  a  con- 
crete surface,  and  does  away  with  the  objectionable  glare  which 
results  when  a  strong  sunlight  shines  on  the  concrete.  The 
bituminous  material  used  is  either  a  refined  tar,  a  tar-asphalt, 
or  an  asphalt  cement.  It  is  applied  to  the  surface  in  the  amount 
of  %  gallon  per  square  yard,  and  spread  by  means  of  hand 


FIG.  137.     Failure  of  a  Bituminous  Surface  on  a  Cement-Concrete  Pavement. 

methods  or  by  distributing  machines.  It  is  considered  that  the 
best  bond  and  most  even  surface  is  secured  by  applying  the  bitu- 
minous material  by  a  pressure  machine  in  two  applications  of 
y±  gallon  each.  The  bituminous  material  is  sometimes  swept 
in  with  either  a  rotary  sweeper  or  with  hand  brooms.  It  is 
then  covered  with  sand  or  fine-stone  chips  to  a  depth  of  ^  to 
l/2  an  inch.  Fig.  137  shows  a  failure  of  a  bituminous  surface  on 
a  cement-concrete  pavement  due  to  the  use  of  a  bituminous 
material  which  would  not  adhere  to  the  concrete. 

COST  DATA.  Cement-concrete  pavements  5  to  6  inches  in 
thickness  usually  cost  between  $1.00  and  $1.80  per  square  yard. 
In  the  following  table  are  given,  for  several  localities  throughout 


326 


ELEMENTS   OF   HIGHWAY    ENGINEERING 


America,  1914  prices  of  cement-concrete  pavements  with  the 
types  of  construction  used  and  the  total  thicknesses  of  the 
concrete. 

From  Engineering  and  Contracting,  April  7,   1915 


City 

Square 
Yards 

Price* 
per 
Sq.  Yd. 

Guar- 
antee, 
Years 

Type 
of 
Pavement 

Thick- 
ness, 
Inches 

Proportions! 

Meriden,  Conn  
Binghamton,  N.  Y  .  . 
Pittsburgh,  Pa  

17,386 
6,439 

2  QSO 

$1.28 
I    52 
I    ^Q 

5 

3 

I  -course 
i  -course 
i  -course 

6K 

6 

2      =4 
i#  :3 

2         '  1 

Sandusky,  O  
Detroit,  Mich  

8,700 
I7O,l6O 

i-3of 

2   28 

5 

2  -course 
2-course 

8 

7 

i#  :3 

1       •  6 

Minneapolis,  Minn.  . 
Kansas  City,  Mo.  .  . 
Lincoln,  Neb  
Columbia,  S.  C  

64,886 
365,323 
1,951 
2,Q6Q 

1.30 

0-973 
1.40 
I    ^5 

5 

2 

i  -course 
i  -course 
2-course 
2-course 

I 

6 
6 

iK  :3 
2K  :4K 
3       :6 

2^4  '  5 

Palo  Alto,  Cal  
Portland,  Ore  
Westmount,  Quebec 

47,600 
68,919 
5,235 

1.22 
I.24f 

2-75 

10 

i  -course 
i  -course 
2-course 

5 
6 
6 

2       :4 
2       :4 
2^  :5 

*  Price  covers  pavement,  foundation  and  shaping  subgrade. 

t  Does  not  include  shaping  subgrade. 

J  Proportions  for  i-course  pavement  or  for  bottom  course  of  2-course  pavement. 

MAINTENANCE 

It  is  not  surprising  that  the  effects  of  traffic  on  concrete 
pavements  are  very  variable,  when  the  variety  of  mixtures  and 
methods  of  construction  used  in  constructing  this  type  of  pave- 
ment in  different  parts  of  the  country  are  considered.  Uneven 
places  may  wear  in  the  surface,  as  shown  in  Fig.  138,  where 
the  concrete  is  not  uniform  in  character.  Unless  careful  super- 
vision is  exercised,  bad  spots  are  very  liable  to  occur,  due  to  a 
poor  mixture  or  a  segregation  of  the  ingredients  when  the 
concrete  is  placed.  Once  such  a  place  starts  to  wear  away,  it 
grows  in  extent  very  rapidly,  the  abrasive  action  of  the  traffic 
grinding  out  the  good  concrete.  Such  places  should,  therefore, 
be  immediately  repaired,  which  is  best  accomplished  by  cutting 
them  out  for  a  depth  of  at  least  3  inches  and  refilling  with  either 
cement  or  bituminous  concrete,  depending  primarily  upon  the 
traffic  conditions.  If  all  loose  material  is  taken  out  of  the  cut  and 
the  surfaces  of  the  opening  are  thoroughly  scrubbed  with  water 
to  remove  the  dust,  it  is  practicable  to  make  an  excellent  patch. 
It  is  useless  to  try  and  level  them  up  with  the  surrounding 


CEMENT-CONCRETE   PAVEMENTS  327 

surface  by  putting  a  little  mortar  in  the  depression.  Places 
where  cracks  have  formed  should  also  be  given  very  close  at- 
tention, since  the  edges  of  the  cracks  and  the  surface  adjacent 
to  them  soon  wear  away.  Filling  the  cracks  with  a  bituminous 
filler  will  serve  to  protect  the  edges  and  prevent  water  from 
seeping  down  through  the  pavement  to  the  subgrade.  Care 


FIG.  138.     Uneven  Wear  of  a  Cement-Concrete  Pavement. 

should  also  be  taken  to  have  the  expansion  joints  always  filled 
flush  with  a  bituminous  filler.  Methods  of  constructing  and 
maintaining  bituminous  surfaces  have  been  explained  in 
Chapter  X. 

CHARACTERISTICS 

A  cement-concrete  pavement  furnishes  a  smooth  surface 
which  is  easy  to  clean  and  is  not  productive  of  much  dust,  but 
it  is  somewhat  noisy.  If  properly  constructed  it  can  carry  a 
heavy  traffic  of  motor  trucks  and  affords  a  fair  foothold  for 
horses.  The  surface  of  the  concrete  can  be  covered  with  a  coat 
of  bituminous  material  into  which  is  rolled  a  layer  of  stone 
chips.  This  treatment  will  serve  to  prolong  the  life  of  the  road, 
will  usually  render  it  non-slippery  under  all  climatic  conditions, 
and  will  make  it  less  noisy. 


CHAPTER  XV 
WOOD  BLOCK  PAVEMENTS 

DEVELOPMENT.  Russia  is  credited  as  being  the  first  country 
to  use  a  pavement  constructed  with  wood  blocks.  Although 
wood  has  been  used  in  this  country  in  the  construction  of  both 
corduroy  and  plank  roads,  neither  type  could  hardly  be  called 
a  wood  pavement  as  the  term  is  now  understood.  The  first 
wood  block  pavements  in  this  country  were  laid  in  New  York 
and  Philadelphia  about  1835,  in  England  about  1838,  and  in 


FIG.  139.     Wood  Block  Pavement  Constructed  with   Round   Cedar  Blocks. 

Paris  about  1880.  The  blocks  first  used  were  round  or  hexagonal 
in  shape.  Round  cedar  blocks  were  extensively  used  in  the  Middle 
West  some  years  ago.  (See  Fig.  139.)  The  patent  office  contains 
many  records  of  different  types  of  wood  block  pavements  that 
were  patented  at  different  times  since  1840.  One  of  the  first 
pavements  in  which  rectangular  blocks  were  used  was  called  the 

328 


WOOD    BLOCK   PAVEMENTS  329 

Nicholson  pavement.  It  was  laid  in  many  cities  jof  this  country 
between  1860  and  1870,  and  was  perhaps  the  most  successful 
wood  pavement  up  to  that  time.  The  blocks,  which  were  3 
inches  thick  and  6  inches  long,  were  laid  in  parallel  courses 
with  i-inch  joints  on  a  plank  subbase  and  the  joints  were  filled 
with  hot  gravel  and  coal  tar.  Little  care  was  taken  in  selecting 
the  wood  for  the  blocks,  and  it  was  not  until  1872  that  a  con- 
crete foundation  was  used.  In  the  development  of  this  type  of 
pavement  it  was  found  that  the  rectangular  block  was  the  best 
shape  to  use,  while  other  details  of  construction,  such  as  proper 
foundation  and  joint  fillers,  were  found  to  have  a  direct  bearing 
on  the  success  of  the  pavement.  It  has  also  been  satisfactorily 
demonstrated  that  the  life  of  the  pavement  is  considerably  in- 
creased if  the  blocks  are  treated  by  some  preservative  process. 
'The  success  of  the  present  type,  which  has  been  developed  by 
the  gradual  improvement  of  the  early  methods  of  construction, 
is  evidenced  by  the  large  amounts  that  have  been  laid  in  Lon- 
don, Paris,  and  the  United  States.  It  has  been  extensively 
used  in  many  of  the  largest  cities  of  this  country,  among  which 
might  be  cited  Greater  New  York,  Philadelphia,  Boston,  Chi- 
cago, Minneapolis,  Detroit,  Cincinnati,  Toledo,  and  Indianapolis. 
It  has  also  proven  to  be  an  excellent  pavement  for  surfacing 
the  roadways  of  bridges,  many  instances  of  which  may  be  found. 

THE  WOOD 

WOODS  COMMONLY  USED.  Very  little  thought  was  given 
to  the  kind  of  wood  used  in  the  earlier  types  of  pavements,  and 
without  doubt  this  fact  hastened  the  failure  of  many  of  the 
pavements  constructed.  The  "Nicholson"  pavement  was  some- 
times constructed  of  blocks  made  of  soft  pine.  Round  cedar 
blocks  were  originally  used  for  paving  the  streets  of  Chicago. 
Among  the  other  woods  which  have  been  used  in  various  cities 
of  the  United  States  may  be  mentioned  oak,  cypress,  hemlock, 
Washington  red  cedar,  cottonwood,  mesquite,  Osage  orange, 
redwood,  Douglas  fir,  tamarack,  long-leaf  yellow  pine,  short- 
leaf  pine,  Norway  pine,  and  black  gum.  A'  great  many  of  the 
wood  pavements  in  England  are  constructed  with  Swedish  deal. 


330  ELEMENTS   OF  HIGHWAY  ENGINEERING 

Experiments  have  been  also  tried  there  with  camphor  wood 
from  Borneo,  oak,  beech,  and  both  Australian  and  American 
red  gum.  The  Australian  woods,  jarrah  and  karri,  which  are 
extremely  hard  and  dense,  were  first  used  in  London  about 
1891.  Now  they  are  used  only  to  a  slight  extent  in  England, 
the  softer  woods  being  preferred.  The  wood  pavements  of 
Australia,  however,  are  largely  constructed  of  jarrah,  which 
is  one  of  the  principal  woods  of  that  country.  In  France,  pine 
of  Landes  and  of  Gascogne  are  used  to  a  great  extent.  Red 
pine  of  Nord,  or  Sylvestre  pine,  commonly  but  improperly  called 
red  fir  of  Nord,  is  also  used.  Little  attention  was  given  to  the 
proper  seasoning  of  the  wood  used  in  the  earlier  pavements, 
and  only  in  rare  instances  were  the  blocks  treated  with  mate- 
rials which  serve  to  preserve  the  wood.  The  importance  of 
these  details  has  been  realized  in  the  development  of  the  modern 
wood  pavement,  so  that  to-day  very  few  blocks  are  laid  which 
are  not  made  from  carefully  selected  wood  and  subjected  to 
some  preservative  process. 

Experience  has  shown  that  there  are  only  a  few  woods  in 
this  country  with  which  it  is  commercially  possible  to  make 
good  blocks.  Specifications  differ  slightly,  but  the  best  practice 
admits  the  use  of  southern  yellow  pine,  Norway  pine,  tamarack, 
and  black  gum.  In  order  to  secure  pavements  of  uniform  quality 
it  is  necessary  to  use  only  good  grade  timber  free  from  loose 
knots,  wrorm  and  knot  holes,  and  shakes. 

CAUSES  OF  DECAY.  The  decay  of  wood  is  due  to  a  low 
form  of  plant  life  called  fungi.  The  fungi  attack  the  wood 
from  the  outside,  and  if  the  wood  is  in  the  right  condition  for 
the  spore  to  grow,  they  will  ultimately  penetrate  the  entire 
structure  of  the  wood.  There  are  three  classes  of  fungi,  one 
of  which  attacks  all  parts  of  the  wood  structure,  another  at- 
tacks the  cellulose,  the  third,  which  is  the  most  common,  attacks 
only  the  lignin,  which  is  the  name  of  the  many  organic  sub- 
stances which  are  incrusted  around  the  cellulose.  The  fungi 
dissolve  the  lignin  and  the  cellulose  and  make  food  for  their 
development.  Heat,  air,  and  moisture  are  all  necessary  for  the 
existence  of  the  fungic  growth. 


WOOD   BLOCK  PAVEMENTS  331 

WOOD  PRESERVATION.  Since  air  and  heat,  in  most  climates, 
are  always  present,  it  is  necessary  to  eliminate  the  moisture 
as  the  first  step  in  destroying  the  fungus  life.  In  fact,  this  is 
partially  accomplished  when  timber  is  seasoned.  The  timber 
is  piled  so  as  to  permit  free  circulation  of  air  around  each  piece, 
and,  in  this  manner,  the  moisture  content  can  be  reduced  from 
15  to  1 8  percent.  Kiln  drying  will  still  further  reduce  the 
moisture  content,  but  timber,  whether  air-dried  or  kiln-dried, 
will  reabsorb  moisture  when  exposed  to  it.  A  more  effective 
method  of  timber  preservation  is  to  treat  the  timber  with  some 
preservative  which  will  change  the  organic  matter  in  the  inner 
structure  so  that  it  will  not  serve  as  food  for  the  fungi.  The 
use  of  a  preservative  treatment  will  not  only  preserve  the  wood 
from  decay  but  will  also  fill  the  pores  and  prevent  the  absorp- 
tion of  other  fluids.  This  is  a  very  desirable  property  for  wood 
blocks  to  possess,  since  it  tends  to  minimize  expansion,  to  increase 
the  resistance  to  wear,  and  to  make  the  pavement  more  sanitary. 

PRESERVATIVES.  The  preservatives  used  are  copper  sulphate, 
zinc  chloride,  creosote,  and  bichloride  of  mercury.  The  process 
of  using  zinc  chloride  is  also  known  as  burnettizing,  and  that 
one  in  which  bichloride  is  used  is  known  as  kyanizing.  The  use 
of  copper  sulphate  has  been  practically  given  up,  and  there 
are  only  a  few  places  which  use  the  bichloride  process,  so  that, 
practically  speaking,  the  processes  in  the  United  States  are 
restricted  to  those  using  creosote  and  zinc  chloride.  Of  these 
two  the  creosoting  process  is  by  far  the  most  common,  and  is 
better,  particularly  if  the  wood  is  to  be  used  where  it  will  be 
wet,  since  the  zinc  chloride  is  soluble  in  water  and  will  leach 
out  of  the  wood. 

Creosote.  Creosote  may  be  obtained  by  the  distillation  of 
coal  tar,  wood  tar,  or  water-gas  tar.  Mixtures  of  coal-tar  creosote 
oils  and  water-gas  tar  creosotes,  creosote  oils  and  resin,  and 
creosote  oils  and  coal-tar  pitch  have  also  been  employed.  It 
has  been  realized  for  some  time  that  the  success  of  a  wood 
pavement  depends  largely  upon  the  character  and  quantity  of 
the  creosote  oil  used  in  treating  the  blocks.  The  function  of 
the  oil  is  to  preserve  the  wood  against  decay  and  prevent 


332  ELEMENTS   OF   HIGHWAY   ENGINEERING 

expansion  and  contraction  for  a  long  period  of  time.  One  of 
the  most  successful  wood  pavements  that  has  been  laid,  the 
Tremont  Street  pavement  in  Boston,  was  constructed  with 
blocks  impregnated  with  a  mixture  of  one-half  creosote  oil  and 
one-half  resin.  Similar  pavements  were  laid  on  the  streets  of 
lower  New  York  up  to  1904.  The  object  of  incorporating  the 
resin  in  the  creosote  was  to  hold  the  preservative  in  the  block. 
In  1907  the  proportion  of  resin  in  the  creosote  was  reduced  to 
25  percent  in  the  New  York  specifications,  and  in  1909  it  was 
decided  that  an  oil  with  a  gravity  of  1.12  did  not  need  the 
resin  component. 

The  creosote  oil  used  abroad  is  lighter,  as  a  general  rule,  than 
that  recommended  for  use  in  this  country,  the  gravity  being 
about  1.07.  In  Paris  and  Germany  some  blocks  are  immersed 
in  a  bath  composed  of  a  mixture  of  coal-gas  tar  and  heavy  oil. 

MANUFACTURE  OF  BLOCKS.  Planks  of  the  required  cross- 
section  are  cut  up  into  blocks  by  a  machine  specially  designed 
for  this  purpose.  The  machine  consists  of  a  series  of  circular 
saws  spaced  at  a  distance  apart  depending  upon  the  size  of  the 
block  to  be  cut.  The  bed  of  the  machine  is  wide  enough  to 
take  a  long  plank,  which  is  cut  into  blocks  by  its  passage  over 
the  saws.  Some  plants  have  a  capacity  as  high  as  240,000 
blocks  per  day.  Fig.  140  shows  an  interior  view  of  the  municipal 
wood  block  plant  in  Paris. 

Size  of  Blocks.  Most  of  the  wood  blocks  are  rectangular  in 
shape  and  are  so  cut  as  to  enable  a  smooth  pavement  to  be 
laid  with  the  rows  of  blocks  of  uniform  width.  It  is  necessary 
to  carefully  specify  the  allowable  variation  from  dimensions  of 
the  block  to  secure  the  desired  results.  A  requirement,  typical 
of  American  practice,  might  read  as  follows:  The  wood  block 
shall  be  rectangular  in  shape  and  of  the  following  dimensions, 
viz.,  not  less  than  6  nor  more  than  9  inches,  but  averaging 
from  7^"  to  8  inches  in  length;  not  less  than  3^  nor  more 
than  4  inches,  but  with  a  maximum  variation  of  not  more  than 
yi  inch  in  width;  not  less  than  3  nor  more  than  4  inches, 
but  with  a  maximum  variation  of  not  more  than  l/t6  inch  in 
depth. 


WOOD   BLOCK   PAVEMENTS 


333 


The  size  of  blocks  used  in  Europe  varies  from  2^.  to  4  inches 
in  width,  from  7  to  11^4    inches   in  length,  and   from   4^/4  to 


FIG.  140.     Saws  at  Municipal  Wood  Block  Plant,  Paris,  France. 

7  inches  in  height.     The  size  used  in  Paris  is  approximately  3 
inches  wide  by  9  inches  long  by  6  inches  deep. 

Treating  the  Blocks.     There  are   two  methods  in  use  for 


334  ELEMENTS   OF  HIGHWAY   ENGINEERING 

impregnating  the  blocks  with  the  preservative  fluid :  the  pressure 
process  and  the  open-tank  process. 

Pressure  Process.  In  the  pressure  process,  which  is  used 
almost  exclusively  in  treating  wood  blocks  in  the  United  States, 
the  blocks  are  placed  in  large  iron  cylinders  which  are  capable 
of  withstanding  pressure.  A  low  steam  pressure  is  maintained 
for  a  time,  which  softens  the  sap.  The  steam,  together  with 
whatever  matter  it  has  dissolved  out  of  the  wood,  is  blown  out 
of  the  cylinder  and  a  vacuum  is  established  which  serves  to 
draw  out  more  of  the  sap  which  has  been  softened  by  the  steam. 
When  this  step  has  been  completed,  the  preservative  fluid  is 
admitted  to  the  cylinder  and  steam  pressure  is  again  applied. 
The  blocks  are  completely  immersed  in  the  oil.  which  is  forced 
into  the  blocks  under  a  sustained  pressure  of  100  pounds  or 
more  per  square  inch  until  the  charge  as  a  whole  has  absorbed 
the  requisite  amount  of  oil.  The  pressure  varies,  depending 
Upon  the  kind  of  wood,  nature  of  the  preservative,  and  the 
amount  it  is  desired  that  the  blocks  shall  absorb.  The  amounts 
of  preservative  used  in  the  United  States  vary  from  16  to  22 
pounds  per  cubic  foot  of  wood.  It  has  been  found  that  it  takes 
on  the  average  about  26  pounds  of  oil  per  cubic  foot  to  make 
a  block  absolutely  waterproof.  For  this  reason  blocks  which 
are  treated  with  a  less  amount  should  be  put  into  place  as 
quickly  as  possible,  so  that  they  will  have  no  chance  to  dry 
out.  On  streets  of  heavy  traffic  16-  to  20-pound  treatments 
have  been  found  satisfactory.  An  amount  as  low  as  10  pounds 
has  been  commonly  used  abroad  in  this  process. 

Open-Tank  Process.  In  the  open-tank  process,  the  blocks 
are  placed  in  a  tank  which  is  filled  with  hot  preservative  and 
left  for  a  period  of  time  which  varies  from  a  few  minutes  to  an 
hour,  depending  upon  the  kind  of  wood  and  the  depth  of  im- 
pregnation desired.  The  tank  is  then  drained  off  and  the  blocks 
are  allowed  to  drip.  This  method  is  used  to  a  large  extent  in 
France. 

Testing  the  Blocks.  The  French  practice  is  to  conduct 
careful  tests  for  resistance  to  wear  when  saturated  with  water, 
resistance  to  compression  and  impact,  and  to  determine  the 


WOOD   BLOCK  PAVEMENTS  335 

amount  of  water  the  treated  wood  will  absorb.  In  this  country 
the  most  common  tests  are  the  amount  of  clear  water  absorbed 
in  a  certain  length  of  time  and  the  analysis  of  the  preservative. 
Water  Absorption.  The  success  of  many  wood  block  pave- 
ments is  attributed  to  rigid  requirements  covering  the  amount 
of  water  which  the  blocks  will  absorb  under  stated  conditions. 
Blow-outs  of  wood  block  pavements  occurring  after  heavy  rains 
have  been  undoubtedly  caused,  in  most  cases,  by  the  absorp- 
tion of  large  amounts  of  water  by  improperly  treated  blocks. 
The  treated  blocks  should  show  such  waterproof  qualities  that, 
after  being  dried  in  an  oven  at  a  temperature  of38°C.  (ioo°F.) 
for  a  period  of  twenty-four  hours,  weighed  and  then  immersed  in 
clear  water  for  a  period  of  twenty-four  hours  and  again  weighed, 
the  gain  in  weight  should  not  be  more  than  3^  percent  when 
tested  at  the  place  where  manufactured  and  not  more  than 

5  percent  when  samples  are  taken  from  the  blocks  delivered 
on  the  work.     Tests  have  shown  that  blocks  will  absorb  some- 
times as  much  as   100  percent  more  water  a  few  weeks  after 
treatment  than  they  will  within  a  few  hours  after  creosoting. 

Amount  of  Preservative  Fluid.  In  order  to  make  sure  that 
the  preservative  treatment  has  thoroughly  impregnated  the 
wood,  several  blocks  in  each  charge  should  be  split  open  and 
examined. 

CONSTRUCTION 

SUBGRADE  AND  FOUNDATION.  The  roadbed  is  excavated 
to  the  required  grade.  It  is  assumed  that  all  subdrains,  catch- 
basins,  inlets,  curbs,  etc.,  have  been  constructed.  The  sub- 
grade  is  shaped  to  the  surface  of  the  finished  pavement  and  is 
carefully  rolled  and  compacted.  Any  poor  material  which  does 
not  compact  properly  should  be  removed  and  replaced  with 
material  of  good  quality. 

On  the  subgrade  is  constructed  the  concrete  foundation,  built 
generally  by  the  mixing  method  as  described  in  Chapter  V. 
The  thickness  of  the  foundation  varies  from  4  to  8  inches,  de- 
pending principally  upon  the  traffic,  the  average  depth  being 

6  inches.     A  thickness  of  9  inches  has  been  recommended  in 


336 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


England  for  streets  subjected  to  the  traffic  of  heavy  motor- 
omnibuses.  The  concrete  foundation,  like  the  subgrade,  is  built 
parallel  to  the  finished  surface  of  the  pavement.  The  amount 
of  crown  to  be  used  can  be  determined  from  the  formulas  in 
Chapter  V.  Fig.  141  shows  a  cross-section  of  a  wood  block 
pavement  as  constructed  in  Pittsburg,  Pa.  It  is  important 
that  the  concrete  should  be  finished  evenly  in  order  to  secure  a 


FIG.    141.     Section    Showing    Construction    of   Wood    Block    Pavement    in 

Pittsburg,  Pa. 

smooth  finished  pavement.  This  can  readily  be  done,  if  the 
stones  are  depressed  and  the  mortar  brought  to  the  surface, 
by  striking  off  the  surface  of  the  foundation  with  a  wooden 
template  before  the  concrete  sets  up.  During  the  time  that 
the  concrete  is  setting  it  should  be  kept  wet,  particularly  in 
hot  weather,  and  in  cold  weather  should  be  protected  from 
freezing. 

CUSHION  LAYER.  The  French  practice  is  to  place  a  thin 
layer  of  mortar  on  the  surface  of  the  concrete  foundation  before 
it  sets  up  and  to  make  this  surface  so  regular  and  smooth  that 
the  wood  blocks  can  be  laid  directly  upon  it  without  any  inter- 
mediate layer  of  material.  The  layer  of  mortar  becomes,  in 
fact,  a  part  of  the  foundation.  The  practice  in  America,  how- 
ever, is  to  place  either  a  layer  of  sand  or  mortar  on  the  concrete 
foundation  after  the  latter  has  set  up.  The  cushion  is  made 
from  %  to  i  inch  in  thickness.  The  object  of  either  kind  of 
cushion  is  to  provide  an  even  surface  in  the  finished  pavement. 
The  mortar  cushion  is  also  used  to  waterproof  the  bottom  of 


WOOD    BLOCK   PAVEMENTS  337 


the  blocks.  A  sand  cushion  may  give  some  Vrouole  if  the 
pavement  is  constructed  with  open  joints,  since  there  is  a 
possibility  of  water  leaching  down  through  the  joints  displacing 
the  sand. 

LAYING  THE  BLOCKS.  The  blocks  are  laid  upon  the  pre- 
pared sand  or  mortar  cushion,  carefully  set  with  the  fibre  of 
the  wood  vertical,  and  in  straight  parallel  courses  at  right  angles 
to  the  edge  of  the  curb.  The  blocks  are  set  loosely  together 
on  the  cushion,  usually  breaking  joints  about  3  inches  with 
no  joints  exceeding  yi  inch  in  width.  Expansion  joints  are 
usually  constructed  parallel  with  and  next  to  each  curb  or  edging. 
The  width  of  each  joint  is  about  one  inch  for  widths  of  20  feet 
and  less  and  is  increased  for  greater  widths.  On  heavy  traffic 
streets  some  engineers  omit  the  expansion  joint.  Many  pave- 
ments, which  have  not  bulged,  have  thus  been  constructed  in 
New  York  City.  The  blocks  are  compacted  by  rolling  with  a 
tandem-roller  of  from  3  to  5  tons  weight  until  the  surface  be- 
comes smooth  and  conforms  with  the  required  crown  of  the 
roadway.  The  success  of  the  wood  block  pavements  in  Min- 
neapolis is  supposed  to  be  due,  in  part,  to  the  fact  that  the  blocks 
are  laid  as  soon  as  possible  after  they  are  received  on  the  street 
and  are  then  kept  wet  by  sprinkling. 

In  the  Middle  West  a  large  amount  of  wood  block  pavement 
is  constructed  by  laying  the  blocks  parallel  to  lines  that  make 
either  an  angle  of  45  or  67^  degrees  to  the  curb  rather  than 
on  lines  at  90  degrees  to  the  curb  line,  as  is  the  practice  in  the 
East.  The  engineers  who  advocate  laying  the  blocks  on  angular 
lines  believe  that  the  pavement  is  benefited  because  the  joints 
are  not  so  severely  exposed  to  blows  of  horses'  hoofs.  These 
claims,  however,  do  not  seem  to  have  been  sufficiently  well 
substantiated  to  warrant  the  general  adoption  of  this  method 
of  laying  the  blocks.  It  is  more  expensive  to  lay  the  pavement 
in  this  manner,  since  skew  blocks  must  be  cut  to  fit  the  curbs 
at  the  ends  of  each  row  of  blocks.  When  the  blocks  are  laid 
on  lines  making  90  degrees  with  the  curb  lines,  specifications 
frequently  require  transverse  expansion  joints,  i  inch  in  width, 
every  50  or  100  feet. 


338  ELEMENTS    OF   HIGHWAY   ENGINEERING 

The  practice  in  Europe  is  to  dip  the  bottoms  of  the  treated 
blocks  in  hot  tar  or  asphalt  and  lay  them  directly  upon  the 
surface  of  the  concrete  foundation,  which  has  been  given  a  per- 
fectly smooth  and  even  surface.  Sometimes  the  foundation  is 
mopped  with  bituminous  material  and  the  blocks  are  laid  directly 
upon  it  without  being  dipped.  By  means  of  strips  of  wood  a 
space  yi  to  ^i  of  an  inch  wide  is  left  between  the  rowrs  of  blocks. 
The  joints  are  filled  with  hot  pitch,  which  is  brushed  out  as 
soon  as  it  is  applied,  so  that  the  joints  remain  only  half  full. 
Clean  gravel,  from  y%  to  ^  of  an  inch  in  size,  is  spread  on  and 
broomed  into  the  joints  so  as  to  fill  the  upper  half  and  enough 
is  left  on  the  surface  to  take  up  the  excess  of  bituminous  mate- 
rial. In  some  instances  the  blocks  are  laid  close  together  and 
the  surface  is  coated  with  a  thin  layer  of  tar  or  tar-asphalt  on 
which  is  spread  a  layer  of  sharp  sand  or  gravel.  This  is  rolled 
in  and  forms  a  durable  coating  that  protects  the  blocks  and 
reduces  slipperiness.  Sand  and  gravel  are  frequently  applied 
to  the  surface  during  the  life  of  the  pavement. 

It  is  the  practice  in  St.  Louis  to  omit  both  the  sand  and  the 
mortar  cushion.  The  concrete  foundation,  which  has  been  pre- 
pared with  an  extremely  smooth  and  regular  surface,  is  given  a 
coat  of  hot  bituminous  material  directly  before  placing  the  blocks 
upon  it.  Each  block  as  it  is  set  into  place  is  dipped  on  one  side 
and  one  end  in  the  same  bituminous  material  that  is  used  to 
cover  the  foundation.  The  side  and  end  of  the  blocks  that  are 
dipped  are  placed  against  the  adjacent  side  and  end  of  blocks 
previously  laid  which  were  not  dipped.  By  this  method  the 
foundation  is  waterproofed  as  well  as  the  underside  of  the  blocks, 
while  the  troubles  arising  from  expansion  are  reduced.  The 
cost  of  laying  blocks  by  this  method  is  more  than  where  either 
the  sand  or  mortar  cushion  is  used. 

FILLING  THE  JOINTS.  After  the  blocks  have  been  thoroughly 
rolled,  the  joints  are  filled  with  a  fine  sand,  a  cement  grout,  or 
some  form  of  bituminous  material. 

Sand  Filler.  According  to  George  W.  Tillson,  M.  Am.  Soc. 
C.  E.,*  "The  first  joint  filler  used  in  modern  wooden  pavements 
*See  Trans.  Am.  Soc.  C.  E.,  Vol.  LXXV,  pages  530-532. 


WOOD   BLOCK  PAVEMENTS  339 

was  sand.  Afterward  Portland  cement  grout  and  bituminous 
fillers  were  used.  The  speaker  has  always  used  sand.  Wood 
blocks  are  so  regular  in  form  that  they  lie  closely  together  in  the 
pavement  and  need  a  filler  only  to  keep  them  in  place.  It  may 
be  said  that  with  a  sand  filler  the  pavement  will  not  be  water- 
proof, but  experience  seems  to  demonstrate  that  the  blocks,  under 
traffic,  soon  mat  together,  making  a  surface  which  is  practically 
continuous.  The  speaker  recently  examined  a  pavement  of  this 
character  which  had  been  subjected  to  light  traffic  for  some 
seven  or  eight  years,  during  which  time  it  had  been  perfectly 
satisfactory.  The  sand  should  be  fine  and  thoroughly  dry 
when  applied,  so  that  the  joints  will  be  entirely  filled.  Should 
oil  at  any  time  exude  from  the  blocks,  the  sand  will  assist  in 
absorbing  it." 

Grout  Filler.  " Where  a  cement  gi?out  is  used,  it  is  made  of 
equal  parts  of  fine  sand  and  the  best  Portland  cement,  care- 
fully mixed,  and  swept  into  the  joints  until  they  are  completely 
filled.  The  pavement  is  then  covered  with  sand,  and  the  grout 
should  be  allowed  to  set  for  at  least  seven  days  before  the  pave- 
ment is  used.  If  the  blocks  are  disturbed  before  the  grout  has 
set,  the  filling  becomes  of  no  more  value  than  sand,  and,  as 
far  as  its  absorptive  properties  are  concerned,  is  even  of  less 
value." 

Bituminous  Filler.  "  Coal- tar  pitch,  asphalt,  and  special 
bituminous  fillers  are  also  used  quite  extensively  by  different 
cities,  the  idea  being  to  make  the  pavement  waterproof  as  well 
as  to  provide  for  some  slight  expansion  of  the  blocks.  Where 
such  fillers  have  been  used  and  excessive  bleeding  has 
occurred,  much  of  it  has  been  attributed  to  the  bituminous 
filler." 

COST  DATA.  Prices  per  square  yard  for  wood  block  pave- 
ments with  5-  to  6-inch  cement-concrete  foundations  usually 
vary  from  $2.50  to  $3.50.  In  the  following  table  are  given, 
for  several  localities  throughout  America,  1914  prices  of  wood 
block  pavements  constructed  with  various  types  of  fillers  and 
different  thicknesses  of  foundations. 


340  ELEMENTS    OF   HIGHWAY   ENGINEERING 


From  Engineering  and  Contracting,  April  7,  1915 


Price* 

Guar- 

Kind 

Concrete 
Foundation 

City 

Yards 

per 

Square 
Yard 

antee, 
Years 

of 
Filler 

Thick-       Propor- 
ness,            tions 
Inches 

Springfield,  Mass  .  .  . 
Meriden,  Conn  
Philadelphia,  Pa  
Pittsburgh,  Pa  
Akron  O 

10,884 

44,331 
31,224 
6,236 
1  8  840 

$3-04 
3-20 
3-28 
3.01 
2  64f 

5 
5 
5 

2 

Sand 
Sand 
Sand 
Cem'tGrout 
Tar 

5          :3      :6 

6          :2y2:5 
6          :3       :6 
6           :3       :6 
6           •  T.       -6 

Chicago  111 

I7QOI4. 

T>     I2t 

? 

Pitch 

6           •  T>       -6 

Detroit,  Mich  
Minneapolis,  Minn.  . 
St.  Paul,  Minn  
Louisville,  Ky  
Portland,  Ore  
So.  Vancouver,  B.  C. 

262,969 
204,655 
269,969 
9J33 

12,108 

65,743 

2.48 

2.40 
2.60 

3-i7t 
2.6of 

3-55 

5 

20 
15 

Tar 
Pitch 
Pitch 
Asphalt 
Cem'tGrout 
Pitch 

6           :3       :6 
5           :3       :6 
5       i:3         5 
6          :3         7 
6:36 
61:3         6 

*  Price  covers  pavement,  foundation,  and  shaping  subgrade. 
t  Does  not  include  shaping  subgrade. 


MAINTL  NANCE 

BLEEDING  OF  PAVEMENTS.  One  of  the  principal  troubles 
with  wood  block  pavements  is  the  oozing  out  of  the  preservative 
fluid,  particularly  during  warm  weather.  (See  Fig.  142.)  The 
bleeding  is  attributed  to  the  character  and  quality  of  the  pre- 
servative fluid  used,  the  effect  of  traffic,  the  expansive  effect 
of  heat  on  the  blocks,  and  the  use  of  too  much  preservative 
fluid  per  cubic  foot.  The  pavement  while  in  this  condition 
is  extremely  objectionable,  but  it  generally  proves  satisfactory 
after  two  or  three  years,  when  the  bleeding  usually  ceases. 
In  Norfolk,  Va.,  where  the  oil  oozed  from  the  surface  of  wood- 
block pavements,  dry  sand  was  applied  and,  when  it  became 
thoroughly  saturated,  was  scraped  off  and  a  second  application 
of  sand  was  made.  The  pavements  in  Norfolk  were  treated 
with  25  pounds  of  preservative  per  cubic  foot.  The  wood 
pavement  on  Market  Street  in  Philadelphia  acted  in  a  similar 
manner.  The  blocks  were  treated  with  24  pounds  of  oil 
per  cubic  foot.  At  the  present  time,  however,  the  pavements 
in  both  of  these  cities  are  in  excellent  condition.  If  the  blocks 
are  properly  treated,  pavements  do  not  generally  ooze  much 
longer  than  the  first  few  months  of  hot  weather,  although  there 


WOOD   BLOCK  PAVEMENTS  341 

are  some  instances  where  pavements  have  oozed  for  four  or 
more  years.  In  these  cases  the  oil  seems  to  run  out,  not  only 
during  hot  weather,  but  also  during  the  early  spring  and  late 
fall. 

REPAIRS  TO  SURFACE.  The  other  maintenance  work  required 
consists  of  removing  poor  blocks  and  of  raising  low  spots  and 
lowering  the  pavement  in  places  which  have  bulged  up.  Places 


FIG.  142.     Bleeding  on  the  Surface  of  a  Wood  Block  Pavement. 

which  have  bulged  up  can  generally  be  attributed  to  the  lack 
of  adequate  expansion  joints.  This  fault  is  accentuated  if  the 
blocks  absorb  water  to  any  great  extent. 

PREVENTION  AGAINST  SLIPPERINESS.  During  wet  and  frosty 
weather  it  will  be  frequently  necessary  to  spread  a  light  coating 
of  sand  over  the  pavement  in  order  to  prevent  it  from  becoming 
slippery.  In  France  and  England,  wood  pavements  have  been 
covered  with  a  bituminous  surface  to  reduce  slipperiness  and 
preserve  the  surface. 

RELAYING.  The  life  of  some  of  the  wood  pavements  in 
Paris  has  been  prolonged  by  taking  up  blocks  after  several 
years  of  service  and  sending  them  to  the  municipal  plant,  where 
the  tops  are  sawed  off  so  that  the  blocks  are  again  of  uniform 


342  ELEMENTS    OF  HIGHWAY   ENGINEERING 

depth,  and  then  relaying  these  blocks  with  the  original  bottom 
surface  as  the  wearing  surface. 

COST  OF  MAINTENANCE.  The  wear  of  wood  block  pave- 
ments is  very  remarkable.  A  block  taken  from  a  street  in 
Chicago,  which  had  been  down  for  six  years  and  subjected  to 
the  traffic  of  many  6-  and  8-ton  loads,  was  found  to  measure 
3.9  inches  on  the  one  end  and  3.85  inches  on  the  other,  its  original 
depth  being  4  inches.  There  are  wood  pavements  in  Chicago 
which  are  ten  years  old  and  apparently  good  for  another  ten 
years. 

There  are  two  wood  paved  streets  in  St.  Louis  which  were 
laid  in  1903  that,  in  1910,  were  in  excellent  condition,  the  total 
repair  charges  on  the  60,000  square  yards  of  pavement  for  the 
seven  years  being  only  $2.10.  The  streets,  while  not  receiving 
the  heaviest  traffic,  are  subjected  to  considerable  hauling  in  the 
form  of  ice,  coal,  and  building  material  wagons. 

In  1900,  Tremont  Street,  Boston,  which  carries  a  heavy 
traffic,  was  constructed  partly  with  wood  block.  In  1915  it 
was  in  very  satisfactory  condition.  Its  life  should  be  between 
twenty  and  twenty-five  years. 

In  Paris,  on  the  streets  which  are  subjected  to  as  many  as 
65,000  teams  per  day,  or  3,400  per  yard  of  width,  the  wear  is1, 
on  the  average,  0.4  of  an  inch  per  year.-  The  average  life  of 
pine-paving  blocks,  which  have  not  been  treated  under  pressure, 
is  about  eight  years.  Some  wood  blocks,  which  have  been  creo- 
soted  under  pressure  have  given  satisfactory  service  for  fifteen 
years. 

CHARACTERISTICS 

A  wood  block  pavement  built  with  blocks,  that  have  been 
treated  with  a  preservative  and  properly  constructed,  makes  an 
excellent  pavement  which  stands  up  under  heavy  traffic.  This 
fact  has  been  substantiated  in  many  places,  not  only  in  this 
country,  but  also  in  France  and  England.  It  is  much  less 
noisy  than  a  stone-block,  brick,  or  an  asphalt  pavement. 
From  the  standpoint  of  the  tenants  of  buildings  along  the  street, 
this  feature  of  a  wood  block  pavement  is  distinctly  appreciated. 


WOOD   BLOCK  PAVEMENTS  343 

Some  teamsters,  however,  object  to  wood  block*  pavement  on 
account  of  its  slipperiness.  It  is  only  fair  to  state  that  this 
condition  is  noticed  principally  at  times  when  the  pavement  is 
in  a  slightly  moist  condition,  but  under  the  same  conditions  it 
is  probably  not  much  more  slippery  than  an  asphalt  pavement. 
When  too  much  preservative  fluid  has  been  used  in  treating 
the  blocks,  some  inconvenience  and  unpleasantness  is  very 
liable  to  be  experienced,  due  to  bleeding.  If  properly  con- 
structed it  presents  a  smooth  surface,  which  is  readily  cleaned. 


CHAPTER  XVI 
BRICK  PAVEMENTS 

DEVELOPMENT.  Probably  the  first  brick  pavements  were 
constructed  in  Holland.  Although  this  type  of  construction 
has  been  employed  in  Holland  for  over  a  century,  the  use  of 
brick  pavements  in  other  parts  of  Europe  is  very  limited.  The 
brick  pavement  was  introduced  into  the  United  States  by  the 
construction  of  a  short  experimental  section  in  Charles  town, 
W.  Va.,  in  1870.  This  was  followed  by  another  experimental 
piece  laid  in  Bloomington,  111.,  in  1875,  and  a  few  other  sections 
laid  from  time  to  time,  up  to  1885,  in  different  cities  of  the 
Middle  West.  Philadelphia  was  the  first  large  city  to  use  brick 
pavement,  a  section  being  laid  in  1887.  The  use  of  this  kind 
of  pavement  then  began  to  increase  rapidly,  and  at  the  pres- 
ent time  there  are  very  few  large  cities  in  the  country  which 
do  not  have  some  of  their  streets  paved  with  this  material.  A 
census  of  the  pavements  laid  in  1910,  in  the  United  States, 
showed  that  brick  was  one  of  the  most  popular  forms  of  pave- 
ment. From  this  census  it  was  found  that  while  sheet  asphalt 
ranked  first  from  the  standpoint  of  yardage  in  the  460  cities 
reported,  brick  was  a  close  second.  It  is  natural  that  the  great- 
est yardage  should  occur  in  those  cities  throughout  the  Cen- 
tral States,  since  this  locality  abounds  with  clay  and  shale 
deposits  suitable  for  the  manufacture  of  paving  brick. 

The  early  brick  pavements  were  constructed  without  a  con- 
crete foundation  and  with  a  sand  filler.  In  the  development  of 
this  type  of  pavement  which  has  taken  place  since  1885,  con- 
siderable attention  has  been  given  to  the  manufacture  of  the 
brick  itself.  Current  practice  usually  requires  a  concrete  founda- 
tion and  generally  some  other  filler  than  sand.  Credit  should 
be  given  to  the  National  Paving  Brick  Manufacturers'  Associa- 
tion for  the  material  improvement  of  methods  of  manufacture 

344 


BRICK   PAVEMENTS  345 

and  many  details  of  construction,  and  the  standardization  of 
the  rattler  test. 

THE  BRICK 

BRICK  CLAYS  AND  SHALES.  A  clay  to  be  used  for  the  manu- 
facture of  brick  should  be  fusible,  plastic,  and  capable  of  being 
heated  to  a  high  temperature  without  losing  its  shape.  Surface 
clays,  therefore,  are  very  little  used,  although  they  are  exten- 
sively employed  in  the  manufacture  of  building  brick. 

Most  of  the  paving  brick  are  now  made  from  shale.  Shales 
are  chemically  of  the  same  composition  as  clays,  but  have  be- 
come hardened  and  have  a  laminated  structure.  They  are 
found  in  large  deposits  in  stratified  beds.  To  make  a  satis- 
factory vitrified  paving  brick  a  shale  should  have  approximately 
the  following  composition,  which  is  an  average  of  fifty  shales 
from  different  sources  that  are  used  for  this  purpose:  silica, 
56  percent;  alumina,  22.5;  water  and  other  volatile  constituents, 
8.5;  and  such  fluxing  constituents  as  sesquioxide  of  iron,  lime, 
magnesia,  etc.,  13.0  percent.  An  excess  of  silica  will  cause 
weakness  and  brittleness,  while  an  excess  of  alumina  will  cause 
shrinking,  cracking,  and  warping. 

MANUFACTURE  OF  BRICK.  The  shales  are  usually  obtained 
by  open  pit  excavations,  a  steam  shovel  being  used  if  the  plant 
is  large  enough  to  warrant  an  outfit  of  this  kind.  The  shale  is 
generally  crushed  by  rolls  4  feet  in  diameter  and  12  inches 
wide  running  within  a  revolving  pan,  9  feet  in  diameter,  that 
has  a  grated  bottom.  The  shale,  as  it  is  crushed,  is  screened 
through  a  4  to  8-mesh  sieve.  The  screened  material  is  mixed 
with  water  in  a  pug  mill  to  the  right  state  of  consistency.  The 
pug  mill  is  a  long  trough  through  which  runs  a  heavy  revolving 
shaft  equipped  with  a  series  of  wide  blades.  The  plastic  shale, 
as  it  leaves  the  pug  mill,  is  forced  by  an  auger  through  a  die 
which  forms  a  continuous  bar  of  stiff  shale  of  the  desired  cross- 
section  and  this  is  cut  into  bricks  of  the  required  size  by  an 
automatic  cutter.  The  dies  and  cutting  apparatus  are  so  ar- 
ranged that  the  bricks  are  cut  off  with  a  side  cut.  In  the  manu- 
facture of  wire-cut-lug-brick,  lugs  are  cut  in  the  sides  by  means 


BRICK  PAVEMENTS  347 

of  wires  travelling  through  guides.  (See  Fig.  143.)  "Vertical- 
fibre"  brick,  which  are  not  repressed,  have  lugs  formed  on  the 
side  by  means  of  the  die.  In  another  method  of  manufacture, 
the  bricks,  after  being  cut  from  the  clay  bar,  are  repressed  in  a 
die,  during  which  process  the  edges  of  the  brick  are  rounded 
off  and  lugs,  grooves,  and  the  brand  mark  are  stamped  on  the 
sides  of  the  brick.  Bricks  made  by  this  method  are  called 
"repressed."  The  function  of  lugs  on  a  paving  brick  is  to  pro- 
vide space  between  the  bricks  for  the  filler.  The  brand  marks 
are  sometimes  raised  and  serve  the  same  purpose  as  lugs. 

The  bricks,  as  they  leave  the  cutting  or  repressing  machine, 
are  piled  on  cars  IrT^snianner  that  will  allow  free  circulation 
of  air  between  them,  and  are  then  hauled  to  a  drying  chamber, 
which  is  heated  either  by  hot  air  or  by  steam  pipes.  It  takes 
from  eighteen  to  sixty  hours  to  dry  the  bricks  properly,  de- 
pending upon  the  kind  of  clay  and  the  plant  arrangement. 
The  bricks  are  burned  from  seven  to  ten  days  at  a  temperature 
of  from  1,500°  to  2,000°  F.,  at  which  temperature  the  clay 
finally  completely  coalesces  or  vitrifies.  It  is  at  this  point  that 
the  brick,  when  slightly  cooled,  has  obtained  its  maximum 
toughness  and  cross-breaking  strength.  The  temperature  which 
is  necessary  to  vitrify  the  brick  is  maintained  in  the  kiln  until 
the  bricks  are  thoroughly  heated  through  to  the  center.  The 
kiln  is  then  tightly  closed  and  the  bricks  are  allowed  to  cool 
off  very  slowly.  This  part  of  the  process  is  called  annealing, 
and  to  obtain  a  tough  brick  requires  from  seven  to  ten  days 
cooling  in  the  kilns.  The  bricks  are  then  sorted  into  different 
lots,  the  No.  i  paving  brick  generally  being  found  in  the  upper- 
most layers  in  the  kiln. 

The  color  of  the  paving  brick  is  governed  largely  by  the 
material  from  which  the  brick  is  made,  the  degree  of  tempera- 
ture which  is  reached  in  vitrifying  the  brick,  and  the  kind  of 
fuel  that  is  used.  The  outside  color  of  a  brick  is  also  changed 
by  the  sand  that  is  used  to  prevent  the  brick  from  sticking  to 
the  dies  or  to  each  other  in  the  kiln.  As  a  rule,  shales  make  a 
brick  either  red  or  brown,  while  the  impurer  clays  give  different 
shades  of  buff. 


348  ELEMENTS   OF  HIGHWAY  ENGINEERING 

SIZE  AND  CHARACTER  OF  BRICK.  Two  sizes  of  brick  are 
used.  The  large  size,  usually  designated  as  blocks,  ordinarily 
has  dimensions  within  the  following  limits:  width,  3  to  3^ 
inches;  depth,  3^  to  4^4  inches;  length,  8>2  to  9^  inches. 
The  average  dimensions  of  the  small  size,  commonly  called 
brick,  are  2^2  inches  in  width,  4  inches  in  depth,  and  8^2  inches 
in  length.  Specifications  usually  allow,  in  a  given  shipment  of 
brick,  a  variation  of  ]/^  inch  in  width  and  depth,  and  X  mcn 
in  length.  The  dimensions  of  vertical-fibre  brick  average 
4  inches  in  width,  8^2  inches  in  length,  and  from  2^ 
to  4  inches  in  depth.  These  brick  are  usually  laid  fiat, 
while  the  types  previously  mentioned  are  ordinarily  laid 
on  edge.  When  the  edges  of  the  brick  are  rounded  the  radius 
should  not  exceed  /{6  inch.  Bricks  should  have  lugs  on  one 
side  only  and  of  such  dimensions  that  the  transverse  joints  will 
be  uniform  in  width,  not  less  than  3/l6  inch  nor  more  than  ^i 
inch.  Practically  all  specifications  require  that  the  brick  should 
be  thoroughly  annealed,  tough,  durable,  regular  in  size  and  shape, 
and  evenly  burned.  When  broken,  the  brick  should  show  a 
dense,  stone-like  body,  free  from  lime,  air  pockets,  cracks,  or 
marked  laminations.  Kiln  marks  should  not  exceed  3/l6  of  an 
inch,  one  edge  at  least  to  show  but  slight  marks.  All  bricks 
so  distorted  in  burning  as  to  lay  unevenly  in  the  pavement 
should  be  rejected.  The  brick  should  always  be  carefully  un- 
loaded by  hand  and  stacked  in  piles  at  the  sides  of  the  streets 
outside  of  the  limits  of  work.  The  number  of  brick  that  it 
will  take  to  make  a  square  yard  of  pavement  depends  upon 
the  size  of  brick  and  the  width  of  joints.  When  laid  flat  about 
35  blocks  per  square  yard  are  required,  and  if  laid  on  edge 
an  average  of  45  blocks  is  used. 

TESTING  THE  BRICK.  It  is  possible  by  means  of  tests  to 
determine  the  quality  of  a  brick  proposed  for  use  in  a  pavement. 
The  most  important  test  employed  is  made  with  the  rattler 
and  gives  some  indication  of  how  the  brick  will  wear  when 
subjected  to  the  action  of  traffic.  The  specifications  of  the 
American  Society  of  Municipal  Improvements  call  for  no  other 
test  than  the  rattler  test  since  it  is  believed  that  if  a  brick  is 


BRICK  PAVEMENTS  349 

sufficiently  hard  and  tough  to  pass  this  test  successfully,  it  is 
of  such  a  quality  that  it  will  successfully  meet  the  requirements 
of  other  tests.  The  other  tests  which  are  sometimes  made  are 
the  absorption,  cross-breaking,  and  crushing-strength  tests. 

The  Rattler  Test.  The  standard  rattler  is  a  machine  which 
consists  essentially  of  an  iron  barrel  about  28  inches  in  diameter 
and  of  about  the  same  length.  The  abrasive  charge  consists  of 
two  sizes  of  spherical  shot,  the  larger  size  being  about  3.75  inches 
in  diameter  when  new,  and  weighing  about  7^  pounds  each, 
the  smaller  size  being  1.875  inches  in  diameter,  and  weighing 
0.95  pound  each.  Ten  of  the  large  shot  are  used  and  enough 
of  the  small  shot  to  bring  the  weight  up  to  a  total  of  300  pounds. 
The  bricks  are  first  dried  for  a  period  of  at  least  th^ee  hours  at 
a  temperature  of  100°  F.  Ten  bricks  are  weighed  and  then 
placed  in  the  rattler  with  the  charge  of  spherical  shot.  The 
rattler  is  revolved  for  1,800  revolutions  at  a  rate  of  29^  to 
30^2  revolutions  per  minute.  The  bricks  are  then  taken  out 
and  their  loss  in  weight  is  determined.  No  .piece  of  brick  should 
be  weighed  which  is  under  one  pound  in  weight. 

Many  specifications  require  that,  in  the  rattler  test,  the 
brick  shall  lose  not  more  than  22  percent  of  their  weight. 
In  order  to  insure  that  brick  of  uniform  quality  is  supplied 
for  a  given  pavement,  in  addition  to  the  above  requirement, 
there  should  be  an  additional  stipulation  that  the  maximum  loss 
in  the  rattler  test  in  any  one  brick  should  not  exceed  27  percent. 
Another  method  of  covering  this  requirement  is  to  state  that 
the  maximum  and  minimum  losses  on  the  individual  brick  should 
not  vary  more  than  ten  points. 

Absorption  Test.  The  absorption  test  is  made  on  five  bricks 
which  have  been  through  the  rattler  test  and  whose  weights 
are  known.  They  are  immersed  in  water  for  forty-eight  hours  and 
then  weighed  again.  From  these  weights,  before  and  after  im- 
mersion, the  percent  of  water  absorbed  can  be  computed. 
Specifications  generally  do  not  allow  over  3^  percent  absorption. 

Cross-Breaking  Test.  The  cross-breaking  test  is  made  by 
placing  a  brick  on  edge  on  supports  which  are  6  inches  apart. 
The  breaking  load  is  applied  at  the  center  of  the  brick.  The 


350  ELEMENTS    OF   HIGHWAY   ENGINEERING 

average  of  the  result  on  ten  bricks  is  used  in  computing  the 
modulus  of  rupture.  R  =  ,  ,2  '  where  W  is  the  average  break- 
ing load  in  pounds,  L  the  length  between  supports  expressed 
in  inches,  b  the  breadth,  and  d  the  depth  in  inches. 

CONSTRUCTION 

SUBGRADE.     The  subgrade  should  be  prepared  with  the  same 
care  that  is  shown  in  building  all  types  of  pavements.    All  poor 


FIG.  144.     Result  of  Constructing  a  Brick  Pavement  on  a  Sand  Foundation. 

material  should  be  replaced  with  material  of  a  good  character 
and  the  whole  thoroughly  compacted  to  correspond  to  the  shape 
of  the  finished  surface  of  the  pavement. 

FOUNDATION.  On  streets  it  is  generally  customary  to  con- 
struct a  brick  pavement  on  a  cement-concrete  foundation,  a 
description  of  which  is  given  in  Chapter  V.  An  average  thick- 
ness for  the  foundation  is  6  inches.  In  constructing  brick  pave- 
ments on  roads  in  Ohio  and  in  Pennsylvania,  a  4-inch  concrete 
foundation  has  been  used.  It  is  believed  by  some  engineers 
that  in  locations  where  the  traffic  is  not  heavy,  either  broken 


BRICK   PAVEMENTS 


351 


stone  or  good  gravel,  well  compacted,  will  serve  satisfactorily  as 
a  foundation.  This  is  not  considered  good  practice.  If  the 
bricks  are' laid  directly  upon  a  sandy  subgrade  the  surface  will 
soon  become  uneven.  (See  Fig.  144.)  The  National  Paving  Brick 


/^"Asphalt 
^     *4- 
-X  6  "4-  Crown  J£"  per  Ft 


VA  Asphalt, 


FIG.  145.      Standard  Section  of  Brick  Pavement,  New  York  State 
Department  of  Highways. 


Courtesy  of  the  Dunn  Wire-Cut-Lug-Brick  Co. 

FIG.  146.     Smoothing  off  the  Sand  Cushion. 

Manufacturers'  Association  specify  two  kinds  of  foundation,  one 
of  concrete  and  the  other  of  No.  2  paving  block,  laid  flat.  The 
latter  foundation  is  constructed  by  covering  the  subgrade  with 
a  layer  of  sand  2  inches  in  thickness  and  laying  the  bricks  flat- 


352  ELEMENTS   OF  HIGHWAY   ENGINEERING 

wise  upon  this  sand  bed,  filling  the  joints  with  a  cement  filler 
composed  of  two  parts  of  clean  sand  and  one  part  of  Portland 
cement.  This  type  of  foundation  has  given  satisfactory  re- 
sults in  some  instances,  but  it  is  almost  as  expensive  to  con- 
struct as  concrete.  When  a  brick  pavement  is  to  be  laid  where 
no  curbs  exist,  a  concrete  shoulder  or  edging  is  built  which 
serves  to  prevent  the  brick  from  moving  laterally  and  holds 
the  sand  cushion  in  position.  Fig.  145  shows  the  standard 
section  used  by  the  New  York  State  Department  of  Highways. 
The  foundation  is  constructed  with  the  same  crown  as  the  sur- 
face. Formulas  for  the  amount  and  distribution  of  the  crown 
have  been  given  in  Chapter  IV. 

CUSHION.  Sandy  material,  which  contains  no  particles  that 
will  not  pass  a  ^-inch  screen,  is  spread  on  the  foundation  in 
such  amount  that  it  will  have  a  thickness  of  \}4  to  2  inches 
when  the  cushion  is  completed.  After  being  carefully  levelled 
off  by  means  of  a  template  so  that  the  surface  of  the  sand  is 
parallel  to  the  finished  surface  of  the  pavement,  it  is  then  rolled 
with  a  light  roller.  (See  Fig.  146.)  Some  cushions  are  prepared 
by  first  rolling  the  sand  and  then  drawing  a  template  over  the 
surface,  the  process  being  repeated  until  a  firm,  even  surface 
is  secured.  A  well  compacted,  even  sand  cushion  is  one  of  the 
most  important  details  in  the  construction  of  brick  pavements. 

LAYING  THE  BRICK.  The  bricks  are  laid  on  the  sand  cushion 
and  generally  at  right  angles  to  the  curb,  except  at  street 
intersections.  If  the  bricks  are  laid  across  the  intersection 
on  lines  at  right  angles  to  the  center  line,  it  is  apparent  that 
the  traffic  entering  from  the  cross  street  will  travel  in  a 
direction  parallel  with  the  long  side  of  the  bricks.  This  causes 
a  greater  wear  at  the  joints  than  when  the  bricks  are  laid  as 
in  Fig.  147. 

When  the  bricks  are  laid  at  right  angles  to  the  curb,  they 
are  placed  on  edge  close  together  with  the  joints  broken  by  at 
least  three  inches.  Care  should  always  be  taken  to  place  the 
lug  sides  on  the  same  side  of  the  course.  On  the  completion 
of  every  fourth  course,  the  brick  should  be  driven  together  so 
as  to  secure  tight  joints  and  straight  courses.  The  end  joints 


BRICK  PAVEMENTS  353 

are  made  tight  by  the  use  of  a  bar  between  the  end  of  each 
row  and  the  curb.  To  avoid  disturbing  the  sand  cushion  the 
laborers  should  stand  on  the  bricks  as  they  are  laid.  The  re- 
quired crown  of  the  pavement  is  obtained  by  the  aid  of  strings, 
stakes,  or  board  templates. 

Rolling.     When  the  pavement  has  been  prepared  as  above 
described,   and   thoroughly  swept,   it  is  ready  for  rolling.     A 


FIG.    147.     One   Method  of  Laying  Bricks  at  Street   Intersections.     Joints 
Filled  with  Asphalt. 

tandem  roller  weighing  not  less  than  3  nor  more  than  5  tons 
is  generally  used.  Rolling  is  commenced  near  the  curb,  the 
roller  travelling  parallel  to  the  curb,  back  and  forth  at  a  slow 
speed  and  gradually  working  across  the  surface  toward  the 
center.  When  the  center  is  reached,  the  roller  starts  at  the 
opposite  curb  and  rolling  again  progresses  to  the  center  as  be- 
fore. Rolling  is  continued  as  described  until  the  bricks  are 
firmly  fixed.  Cross  rolling  is  usually  required  wherein  the  roller 
travels  in  a  direction  at  45  degrees  from  curb  to  curb  and  then 
in  the  opposite  45-degree  direction.  Any  broken  or  unsatis- 
factory brick  which  are  found  during  the  work  of  rolling  are 
replaced.  Upon  completion  of  the  rolling,  the  surface  may  be 


354  ELEMENTS   OF  HIGHWAY   ENGINEERING 

tested  with  a  lo-foot  straight  edge.  Some  specifications  require 
the  removal  and  relaying  of  any  parts  that  show  a  depression 
exceeding  %  of  an  inch  when  tested  by  this  method. 

EXPANSION  JOINTS.  To  allow  for  expansion  of  the  pave- 
ment it  is  common  practice  to  insert  boards  between  the  curb 
and  the  pavement  which  will  provide  a  space  from  i  to  ij^ 
inches  wide.  After  the  pavement  is  otherwise  completed,  the 
board  or  boards  are  removed  and  this  space  is  thoroughly  cleaned 
out  and  filled  with  a  bituminous  filler.  Some  specifications  also 
provide  for  a  transverse  expansion  joint,  constructed  in  a  similar 
manner,  at  a  distance  of  every  25  to  50  feet.  Transverse  ex- 
pansion is  sometimes  provided  for  in  a  cement  grout-filled  pave- 
ment by  filling  with  a  bituminous  filler  the  joints  of  four  to  six 
adjacent  rows  of  blocks  about  every  25  feet  along  the  street. 
Unless  great  care  is  taken  in  providing  for  the  expansion  of 
the  pavement,  serious  trouble  may  ensue,  particularly  where  the 
pavements  are  subjected  to  marked  changes  of  temperature. 
If  the  pavements  are  constructed  in  the  hottest  months  of  the 
year,  the  bricks,  being  in  an  expanded  condition  when  laid, 
will  not  expand  as  much  after  the  pavement  is  constructed  as 
when  they  are  laid  in  a  cold  season.  When  a  brick  pavement 
cannot  expand  in  its  normal  plane,  the  brick  wearing  course 
arches  up  over  the  sand  cushion.  The  pavement  under  this 
condition  becomes  noisy,  and  frequently  cracks  are  formed  in 
the  surface.  In  some  cases  the  expansion  is  sufficient  to  force 
the  pavement  up  several  feet. 

JOINT  FILLERS.  After  the  pavement  has  been  rolled,  the 
joints  should  be  filled  with  some  suitable  material.  Sand,  cement 
grout,  coal-tar  pitch,  and  asphalt  have  been  used  as  joint  fillers. 

Sand  was  used  for  a  joint  filler  in  the  earliest  type  of  brick 
pavements.  In  many  places  where  traffic  was  not  heavy,  it 
was  successful,  but  it  does  not  protect  the  joints  from  wear 
nor  does  it  provide  a  waterproof  surface. 

Cement  grout  filler  is  strongly  recommended  by  the  National 
Paving  Brick  Manufacturers'  Association.  This  type  of  filler, 
however,  is  difficult  to  apply.  If  improperly  used  successful 
results  cannot  be  expected.  To  quote  Will  P.  Blair,  Secretary 


BRICK  PAVEMENTS  355 

of  the  National  Paving  Brick  Manufacturers'  Association,  "the 
following  practices  have  come  under  my  observation:  I  have 
seen  the  filler  dipped  from  the  mixing  box  with  a  bucket  and 
carried  many  steps.  In  such  case,  the  sand  was  on  its  way  to  the 
bottom  of  the  bucket  and  the  cement  was  making  for  the  top. 

"I  have  seen  the  mixture  placed  in  a  cradle  or  rocking  box 
and  in  the  time  intervening  the  turning  of  the  box,  the  sand 
and  cement  were  undergoing  a  like  separation,  and  as  the  box  was 
turned  the  richer  mixture  of  cement  flowed  ahead  and  the  weaker 
and  sandy  portion  remained  near  the  box. 

"I  have  seen  the  water  applied  before  the  mixture,  in  a  dry 
state,  reached  an  even  shade,  thus  preventing  the  proper  ad- 
hesion of  the  particles. 

"To  remedy  the  thickening  of  the  mixture,  I  have  seen  it  en- 
tirely ruined  by  throwing  upon  the  street  the  water  from  an  open 
nozzle,  which  served  only  to  float  the  cement  away  from  the  sand. 

"I  have  seen  the  mixture  put  upon  the  street  much  faster 
than  it  could  be  swept  in. 

"I  have  seen  the  mixture  prepared  in  a  dry  street  in  large  quan- 
tities at  intervals  of  a  few  feet  upon  the  brick,  and  the  water  applied 
and  the  sweeping-in  process  undertaken  simultaneously. 

"I  have  seen  the  mixture  made  up  in  such  large  batches 
that  it  required  a  sweeping  of  several  feet  before  it  could  be 
made  to  disappear  in  the  interstices.  In  such  cases,  the  last 
that  went  in  was  but  very  little  better  than  pure  sand. 

"I  have  taken  a  quantity  of  sand  from  the  supply  to  be  used 
for  filler  purposes  and  found  that  it  contained  33  percent  of 
soil.  Thus  I  might  enumerate  for  hours  the  manner,  method, 
and  means  of  applying  the  cement  filler  in  the  interstices  of  a 
brick  street,  each  and  every  one  of  which  was  but  to  insure 
failure,  and  in  none  of  which  is  economy  to  the  contractor 
subserved." 

Trouble  which  may  arise  from  expansion  of  grout-filled  pave- 
ments has  already  been  mentioned.  Fig.  148  shows  a  poor 
brick  in  a  grout-filled  pavement.  To  remove  this  brick  will 
probably  require  the  destruction  of  at  least  two  of  the  adjacent 
bricks.  Fig.  149  shows  how  the  cement  grout  is  chipped  out 


356 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


between  some  joints  by  the  horse-drawn  traffic.    Fig.  150  shows 
a  grout-filled  pavement  which  has  expanded  longitudinally  and 


FIG.  148.     Poor  Brick  in  a  Cement  Grout-filled  Pavement 


FIG.  149.     Chipping  Out  of  Grout  Filler  in  the  Joints  by  Horse-drawn  Traffic. 

slightly  arched  up  at  more  or  less  regular  intervals,  the  limits 
of  which  are  marked  by  the  dark  transverse  streaks  in  the 
photograph.  Fig.  151  shows  a  properly  cement  grout-filled 


FIG.  150.     Longitudinal  Expansion  in  a  Grout-filled  Pavement. 


FTG.    151.      Cement 


Courtesy  of  the  Dunn  Wire-Cut-Lug-Brick  Co. 

Grout-filled    Wire-Cut-Lug-Brick    Pavement    on    New 
York  State  Highway. 


358 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


pavement.  Fig.  152  is  a  construction  view  showing  the  way  the 
grout  is  applied  in  filling  the  joints  according  to  approved  methods. 

The  use  of  some  types  of  bituminous  filler  presents  several 
advantages.  No  transverse  expansion  joints  are  necessary  and 
a  large  amount  of  the  expansion  troubles  are  eliminated.  The 
pavement  can  be  used  as  soon  as  it  is  constructed,  whereas 
when  a  grout  filler  is  used  the  pavement  must  be  kept  closed 
to  traffic  for  a  period  of  from  ten  days  to  two  weeks.  Another 
advantage  of  the  bituminous  filler  is  that  in  making  any  open- 
ings in  the  pavement,  the  bricks  can  be  taken  out  with  less 
breakage  than  where  the  joints  are  filled  with  a  cement  grout. 
Due  to  the  fact  that  there  is  very  little  trouble  from  expansion, 
the  pavement  is  less  noisy.  Fig.  147  shows  the  surface  of  a  brick 
pavement  properly  constructed  with  a  bituminous  filler.  Fig. 
153  shows  a  joint-filler  can,  which  is  conical-shaped  and 
equipped  with  a  rod  to  regulate  the  flow  of  the  material.  With 
this  type  of  can  excellent  results  can  be  obtained. 

COST  DATA.  The  cost  per  square  yard  of  brick  pavement 
and  a  6-inch  cement-concrete  foundation  varies  from  $1.75  to 
$2.75.  In  the  following  table  are  given,  for  several  localities 
throughout  America,  1914  prices  of  brick  pavements  constructed 
with  various  types  of  fillers  and  different  thicknesses  of  sand 
cushions  and  cement-concrete  foundations. 

From  Engineering  and  Contracting,  April  7,   1915 


City 

Square 
Yards 

Price* 
per 
Square 
Yard 

Guarantee, 
Years 

Kind  of 
Filler 

Sand  Cushion 
Thickness, 
Inches 

Concrete 
Foundations 

Thickness 
inches 

Propor- 
tions 

Pittsfield,  Mass  .... 
Syracuse,  N.  Y  
Philadelphia,  Pa.  ... 
Pittsburgh  Pa 

1,130 

87,720 
80,762 
11,829 
100,728 
68,514 
66,619 
42,099 
10,634 
82,962 
34,184 
38,417 

$2.90 
2.  19 
2.74 
2.01 
1-63 

I   87f 

2.  Ilf 

i-85t 
2.25 
i-78t 
2-34t 

2.07f 

5 
2 

5 

i 

5 
5 
5 

5 
20 

10 

Cement  Grout 
Cement  Grout 
Cement  Grout 
Bituminous 
Tar 
Asphalt 
Asphalt 
Cement  Grout 
Asphalt 
Cement  Grout 
Cement  Grout 
Cement  Grout 

i% 

\% 

2 

I# 

2 

i# 

i# 

i 

i# 

6 
6 
6 
6 
5 
5 
5 
6 

5 
6 
6 
5 

:3  :6 
:3  :6 

:3  :6 
:3  :6 
:3  =5 
:3^:6 
:3  :6 
•>3l/2--7 
:3  :6 
:3  7 
:3  :6 
:3  =7 

Canton  O 

Toledo  O 

Moline,  111  
Grand  Rapids,  Mich. 
Minneapolis,  Minn. 
Louisville,  Ky  
Portland,  Ore  
Toronto,  Ont  

*  Price  covers  pavement,  foundation,  and  shaping  subgrade. 
t  Does  not  include  shaping  subgrade. 


Courtesy  of  the  Dunn  Wire-Cut-Lug-Brick  Co. 

FIG.  152.     Application  of  Cement  Grout  Filler. 


'IG.  153.     Asphalt  Filler  Pouring  Can 


360  ELEMENTS  OF  HIGHWAY  ENGINEERING 

MAINTENANCE 

The  maintenance  of  a  brick  pavement  consists  mainly  -in 
replacing  poor  brick,  repairing  joints  and  rectifying  any  low 
spots  which  appear  in  the  surface  due  to  poor  drainage  and 
foundation.  When  heaving  occurs  due  to  expansion,  the  pave- 
ment may  bulge  up  and  necessitate  extensive  repairs.  Some- 
times by  cutting  out  one  or  two  rows  of  bricks  the  pavement 
will  settle  down  again  on  the  sand  cushion.  In  Minneapolis, 


FIG.   154.     Cleaning  Joints   Prior  to   Application   of   Bituminous   Material. 

where  the  surface  of  a  brick  pavement  had  become  somewhat 
rough,  due  either  to  the  uneven  wear  of  the  brick  or  to  wear 
at  the  edges,  a  bituminous  surface  was  applied  and  covered 
with  a  layer  of  screened  chips.  This  surface  has  not  only  served 
to  protect  the  brick  from  further  wear  but  has  also  improved 
the  foothold  and  lessened  the  noise  of  traffic.  See  -Figs.  154 
and  155.  Brick  pavements  can  be  found  that  have  been  in 
use  for  twenty  years  and  are  still  in  good  condition.  Where  the 
traffic  conditions  are  not  too  severe  and  the  pavement  has 
been  properly  constructed,  a  brick  pavement  will  wear  for  a 
long  time  with  practically  no  expense  for  maintenance,  pro- 
vided the  forces  of  contraction  and  expansion  are  not  sufficient 
to  disrupt  the  surface. 


BRICK   PAVEMENTS  361 


CHARACTERISTICS 

A  brick  pavement,  when  properly  constructed  on  a  concrete 
foundation,  is  very  durable  unless  the  traffic  is  extremely  heavy. 
If  properly  built  with  a  bituminous  or  cement  grout  filler  the 
surface  wears  smooth,  offers  light  resistance  to  traction,  is  easy 
to  clean,  produces  no  dust,  and  furnishes  a  fair  foothold  for 
horses.  If  proper  allowances  are  not  made  for  expansion  and 
contraction  when  cement  grout  filler  is  used,  the  pavement  is 


FIG.  155.     Surface  of  Badly  Worn  Brick  Pavement,  Showing  Condition,  After 
Three  Years'  Service,  of  Joints  Repaired  with  Asphalt  Filler. 


liable  to  arch  itself  above  the  sand  cushion  and  become  noisy, 
which  is  a  decided  objection.  A  bituminous  filler  prevents 
the  occurrence  of  such  a  condition,  but  unless  the  proper  kind  of 
bituminous  filler  is  used,  the  edges  of  the  bricks  wear  and  round 
off  under  the  action  of  traffic.  In  some  of  the  smaller  cities, 
brick  pavements  have  been  successfully  used  for  business 
streets,  while  in  some  of  the  largest  cities  its  use  is  restricted  to 
residential  streets.  Although  in  Chapter  IV  it  was  stated  that 
a  maximum  grade  of  about  5  percent  was  adopted  for  brick 
pavements  in  some  localities,  this  type  of  pavement  has  been 
used  on  much  steeper  grades.  In  fact,  in  1910,  there  were 


362  ELEMENTS   OF   HIGHWAY   ENGINEERING 

several  instances  where  brick  pavements  were  constructed  on 
grades  of  10  percent  and  more.  If  a  grout  filler  is  used  on 
steep  grades,  the  pavement  may  become  very  slippery.  A  bitu- 
minous filler  will  be  found  to  be  of  material  advantage  in  such 
cases.  In  the  1915  highway  specifications  of  the  Board  of  Water 
Supply  of  New  York  City,  hillside  blocks  or  blocks  having  one 
edge  bevelled  are  required  on  grades  of  over  5  percent. 


CHAPTER  XVII 
STONE  BLOCK  PAVEMENTS 

DEVELOPMENT.  According  to  existing  records,  stone  block 
was  the  first  material  used  for  paving  roadways.  A  historical 
review  of  the  types  used  prior  to  about  A.D.  1840  has  already 
been  covered  in  Chapter  I.  As  stated  in  that  chapter,  Telford, 
in  1824,  was  apparently  the  first  to  recognize  the  value  of  a 
stable  foundation  and  small  size  blocks  cut  in  such  a  manner 
as  to  give  close  joints.  London  appears  to  be  the  first  city  to 
develop  this  type  of  pavement.  Mortar  joints  were  first  used 
in  1840,  while  later,  about  1872,  a  method  of  construction  was 
adopted  in  which  a  concrete  foundation,  and  tar  and  gravel 
joints  wrere  employed. 

Belgian  block  pavement  was  used  in  European  cities  about 
the  middle  of  the  nineteenth  century,  while  in  1859  it  came  into 
common  use  in  New  York.  Belgian  blocks,  so-called  because 
they  were  first  used  in  Belgium,  were  similar  to  truncated  pyra- 
mids in  shape,  having  bases  of  5  to  6  inches  square,  and  depths 
of  from  7  to  8  inches.  As  it  was  impossible  to  maintain  a  smooth 
surface  with  these  irregular  shaped  blocks,  the  rectangular  block 
pavement  was  ultimately  adopted.  This  shape  of  block  was 
first  used  in  New  York  City  about  1876.  Due  to  the  fact  that 
the  first  Belgian  block  pavements  laid  in  New  York  were  con- 
structed with  blocks  of  trap  rock  taken  from  the  Palisades  on 
the  Hudson,  all  trap  rock  block  pavements  were  called  Belgian 
block  pavements,  regardless  of  the  shape  of  the  block. 

In  the  more  recent  development  of  the  rectangular  stone 
block  pavement  more  attention  has  been  paid  to  the  surface 
finish  and  sizes  of  the  blocks,  the  joint  filler,  and  the  foundation. 
The  blocks  are  generally  required  to  be  laid  on  a  concrete  founda- 
tion, and  sand,  tar  and  gravel,  pitch,  asphalt,  and  cement  grout 
are  used  as  fillers.  Within  the  past  few  years  the  use  of  small 

363 


364  ELEMENTS   OF   HIGHWAY   ENGINEERING 

block  pavements  has  developed  in  certain  parts  of  Europe. 
Both  4-inch  cubes  and  smaller  setts,  approximating  2^-inch 
cubes,  have  been  employed  in  this  construction. 

STONE  BLOCKS 

THE  STONE.  The  blocks,  while  generally  being  made  from 
granite,  are  sometimes  cut  from  sandstone,  quartzite,  and 
trap  rock.  The  stone  blocks  should  be  of  such  quality  that 
they  will  resist  shocks,  crushing,  and  weathering  and  will  not 
wear  round  and  smooth  under  the  action  of  traffic.  They  should 
be  of  uniform  quality  and  texture,  without  seams,  scales,  or 
discolorations. 

The  planes  of  cleavage  of  granite  are  such  that  it  is  easy  to 
make  blocks  from  it.  The  trap  rocks  are  harder  and  tougher 
than  the  granites  and  are  not  so  easily  made  into  blocks.  Sand- 
stone blocks  are  not  usually  suitable  for  streets  taking  very 
heavy  traffic.  They  do  not  wear  round  like  the  granite  blocks, 
but  more  uniformly,  although  sometimes  very  rapidly.  The 
Medina  and  Potsdam  sandstones,  which  are  found  in  New  York 
State,  have  been  used  in  pavements  to  a  considerable  extent 
throughout  the  State.  In  Rochester,  N.  Y.,  dressed  Medina 
stone  has  been  used  with  excellent  results  on  the  main  streets 
taking  a  heavy  traffic.  A  large  amount  of  quartzite  has  been 
laid  in  Chicago  with  good  results. 

MANUFACTURE  OF  THE  BLOCKS.  The  majority  of  stone  blocks 
are  made  with  hand  tools.  Large  blocks  of  stone  are  split  up 
into  sizes  desired  by  the  use  of  plugs  and  feathers.  The  faces 
of  the  blocks  are  then  hammer-dressed  until  smooth  enough  to 
comply  with  the  specifications.  The  small  sized  blocks  used  in 
the  construction  of  Kleinpflaster  and  Durax  pavements  are  cut 
out  by  the  machine  shown  in  Fig.  156. 

Considerable  care  has  to  be  taken  in  making  blocks  for  a 
first-class  pavement.  The  blocks  should  be  dressed  so  as  to  be 
rectangular  on  the  faces,  having  parallel  sides  and  ends  with 
approximately  right  angle  edges.  Some  specifications  do  not 
allow  depressions  on  the  face  exceeding  ]/^  of  an  inch.  If  the 


Courtesy  of  the  Wern  Machinery  and  Engineering  Co. 

FIG.  156.     Machine  Used  for  Cutting  Durax  and  Kleinpflaster  Blocks. 


366  ELEMENTS   OF  HIGHWAY   ENGINEERING 

faces  are  very  rough,  it  is  impossible  to  obtain  close  and  even 
joints  in  the  pavement. 

SIZE  OF  BLOCKS.  The  size  of  blocks  is  quite  variable.  In 
the  United  States  large  standard  blocks  for  a  first-class  pavement 
are  from  5  to  8  inches  deep,  3  to  4^  inches  wide,  and  from 
8  to  1 2  inches  long.  A  block,  4  to  4^  inches  deep,  3^  to  4  inches 
wide,  and  6  to  12  inches  long,  is  used  by  some  engineers  on 
steep  grades  as  a  continuation  of  broken  stone  roads,  brick, 
wood  block,  bituminous  concrete,  and  other  types  of  bituminous 
pavements. 

In  Liverpool,  England,  blocks  for  heavy  traffic  streets  are 
6  inches  deep,  3  inches  wide,  and  5  to  6  inches  long.  In  Birming- 
ham, England,  blocks  which  are  approximately  4-inch  cubes  are 
used.  The  stone  blocks  used  in  France  are  either  cubical  or 
rectangular  in  shape  and  of  very  variable  dimensions,  the  lengths 
varying  from  6  to  9  inches,  the  widths  from  4  to  8  inches,  and 
the  depths  from  6  to  9  inches. 

The  rough  cubical  blocks  for  Kleinpflaster  and  Durax  pave- 
ments are  somewhat  similar  in  size.  Those  for  Kleinpflaster 
are  about  2^  by  2^  by  2j^  inches  while  the  blocks  for  the 
Durax  pavement  vary  from  2^  to  3^  inches. 

TESTS  FOR  STONE  BLOCK.  No  standard  tests  for  the  physical 
properties  of  stone  block  have  been  adopted  in  the  United 
States.  The  qualities  of  the  stone  of  which  a  block  is  com- 
posed, however,  can  be  determined  by  submitting  it  to  the 
abrasion,  hardness,  and  toughness  tests  as  made  on  rock  from 
which  broken  stone  is  manufactured.  These  tests  have  been 
described  in  Chapter  VIII.  The  crushing  strength  of  the  stone 
is  the  only  characteristic  that  is  determined  by  some  engineers. 

CONSTRUCTION 

SUBGRADE  AND  FOUNDATION.  The  subgrade  should  be  pre- 
pared according  to  the  same  general  directions  that  have  been 
given  in  previous  chapters.  Since  a  stone  block  pavement 
is  usually  the  type  recommended  to  take  the  heaviest  kind  of 
commercial  traffic,  a  cement-concrete  foundation  should  be  used. 


STONE  BLOCK  PAVEMENTS  367 

Different  methods  of  constructing  concrete  foundations  have 
been  described  in  Chapter  V.  Although  the  mixifig  method  is 
the  one  generally  used,  in  certain  parts  of  the  country  the 
grouting  method  has  been  used  to  a  considerable  extent  in  con- 
structing foundations  for  this  type  of  pavement.  Unless  stone 
block  pavements,  which  are  constructed  on  sand,  gravel,  or 
broken  stone  foundations,  are  given  constant  attention,  the 
blocks  soon  get  out  of  place,  the  edges  of  the  blocks  become 
rounded  off,  the  surface  becomes  very  uneven,  and  ultimately 
the  pavement  reaches  a  condition  where  it  is  not  much  better 
than  one  composed  of  cobblestones. 

Kleinpflaster  and  Durax  pavements  have  been  built  on  con- 
crete foundations.  These  types  of  small  block  pavements  have 
also  been  built,  when  subjected  to  light  traffic,  on  foundations 
of  broken  stone,  gravel,  and  on  aid  broken  stone  roads  which 
have  been  properly  shaped  up. 

The  surface  of  the  foundation  is  usually  constructed  parallel 
to  the  surface  of  the  finished  pavement.  In  Chapter  IV  will 
be  found  formulas  giving  the  amount  and  distribution  of  the 
crown. 

CUSHION  LAYER.  A  cushion,  composed  of  dry,  clean  sand, 
is  spread  on  the  concrete  foundation  previous  to  laying  the 
blocks.  The  purpose  of  the  cushion  is  to  hold  the  blocks  at 
the  bottom,  to  make  practical  the  laying  of  blocks  of  uneven 
depth,  and  to  take  up  any  small  irregularities  in  the  foundation. 
The  thickness  of  the  cushion  will  depend  somewhat  upon  the 
character  of  the  blocks  used,  2  inches  being  a  common  value 
when  the  blocks  are  quite  regular  in  shape. 

LAYING  THE  BLOCKS.  The  blocks  are  placed  on  the  sand 
cushion  as  closely  as  possible,  usually  in  straight  parallel  courses 
with  the  long  dimensions  perpendicular  to  the  curbs.  The  paver 
uses  a  special  form  of  hammer,  one  end  of  which  has  a  flat 
blade.  He  scoops  out,  with  the  blade  end  of  the  hammer,  a 
place  in  the  sand  cushion  for  the  block  to  rest  in,  places  the 
block  and  hits  it  a  few  taps,  so  that  its  surface  is  even  with  that  of 
the  adjacent  blocks.  (See  Fig.  157.)  The  blocks  in  one  row  should 
break  joints  with  the  blocks  in  another  row  by  at  least  3  inches. 


368 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


At  street  intersections,  in  order  to  prevent  the  traffic  of  the 
cross  streets  from  travelling  parallel  to  the  long  joints  and 
thus  forming  grooves,  the  blocks  are  laid  with  their  long 
dimensions  parallel  to  one  or  both  of  the  diagonals  of  the  square 
formed  by  the  intersecting  streets.  The  blocks  may  be  laid 
to  the  desired  crown  by  the  use  of  strings,  cross-section  stakes, 
or  a  board  template.  After  placing  the  blocks  to  the  proper 


FIG.  157.     Construction   of  Stone  Block  Pavement  in  Hamburg,  Germany. 


lines  they  are  thoroughly  tamped  with  a  tamper  weighing  from 
60  to  70  pounds  until  no  further  settlement  occurs.  The  joints 
are  then  filled  with  the  material  which  has  been  selected  for 
this  purpose.  Fig.  158  is  a  cross-section  of  a  stone  block  pave- 
ment as  constructed  by  the  City  of  Pittsburg,  Pa.,  and  serves 
to  show  the  general  arrangement  of  the  foundation,  the  cushion 
layer,  and  the  blocks. 

The  small  setts  of  Kleinpflaster  and  Durax  pavements  are 
laid  in  circular  or  parabolic  arcs,  see  Figs.  159  and  160,  hence 
the  joints  are  continually  broken  in  the  direction  of  travel,  thus 
reducing  the  noise  of  traffic. 

FILLING  THE  JOINTS.  Sand,  tar  and  gravel,  pitch,  asphalt, 
and  cement  grout  are  used  to  fill  the  joints  of  stone  block  pave- 


STONE   BLOCK   PAVEMENTS 


369 


ment.  The  object  of  the  filler  is  to  make  the  pavement  water- 
proof, to  completely  fill  the  joints  in  order  to  eliminate  recesses 
in  which  filth  might  collect,  and  to  protect  the  edges  of  the  block. 


FlG.   158.     Cross-section  Showing  Construction    of 
Stone  Block  Pavement,    Pittsburg,  Pa. 


Sand  should  not  be  used  as  it  does  not  satisfy  any  of  the 
functions  of  an  efficient  filler. 

Tar  and  gravel,  pitch  and  asphalt  have  all  been  satisfactorily 
used  for  fillers.  It  is  absolutely  necessary,  however,  that  the 


FIG.  159.     Construction  of  a  Durax  Pavement  near  London. 

bituminous  filler  should  possess  such  properties  that  it  will  not 
soften  to  the  point  of  flowing  in  summer  nor  harden  in  winter 
so  that  it  will  be  brittle  and  chip  out  under  the  blows  of  horses' 
feet.  The  use  of  a  bituminous  filler  makes  the  pavement  less 
noisy  than  when  a  grout  filler  is  used  and  enables  repairs  to  be 


370 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


made  at  a  minimum  cost,  as  the  blocks  may  be  readily  removed. 
Cement-grout  filler,  when  properly  mixed  and  applied,  has 
given  very  satisfactory  results  from  the  standpoints  of  producing 
a  sanitary  pavement  and  protecting  the  edges  of  the  block. 
It  does,  however,  materially  increase  the  slipperiness  of  the 
surface  and  makes  repairs  for  street  openings  expensive  and 
difficult,  as  the  blocks  have  to  be  broken  up  in  order  to  remove 
them,  and  it  is  impracticable,  in  many  cases,  to  keep  traffic  off 


FIG.  160.     Surface  of  Durax  Pavement  on  the  Chelsea  Embankment,  London. 


the  repairs  until  the  grout  has  set  up.  Many  improperly  grout- 
filled  granite  block  pavements  have  become  rough  within  a  few 
years  due  to  the  cement  grout  being  rapidly  chipped  out  by  the 
blows  of  horses'  feet. 

The  methods  of  using  bituminous  and  cement  grout  fillers 
have  been  described  in  Chapter  XVI. 

COST  DATA.  The  average  cost  of  constructing  stone  block 
pavements  on  a  Portland  cement-concrete  foundation,  5  to  6 
inches  thick,  varies  from  $2.50  to  $3.75  per  square  yard.  In 
the  following  table  are  given,  for  several  localities  throughout 
America,  the  average  1914  prices  of  stone  block  pavements 
constructed  with  various  types  of  fillers  and  thicknesses  of 
foundations. 


STONE   BLOCK   PAVEMENTS 


371 


From  Engineering  and  Contracting,  April  7,  1915 


j 

f  
Concrete 

rrice- 

K-inrl   of 

Foundation 

City 

Yards 

Square 

S£j 

Filler 

Thick- 

Propor- 

Yard 

£*•>• 

ness,  In. 

tions 

Cambridge,  Mass.         8,584 

$3-75 

Cement  Grout 

6 

3      :.S 

Maiden,  Mass.  .  .  .       13,388 

2.96 

5 

Cement  Grout 

5              2^:5 

Worcester,  Mass.  . 

2O,6oi 

3-35 

Cement  Grout 

5 

3      :6 

Providence,  R.  I  .  . 

10,327 

3-34 

Cement  Grout 

6 

3      :6 

Buffalo,  N.  Y  

5,892 

3-96 

10 

Cement  Grout 

6 

10 

Brooklyn,  N.  Y..  . 

112,622 

3-46 

i 

Tar 

6 

3      :6 

Elizabeth,  N.  J  .  .  . 

81,828 

3-35 

5 

Cement  Grout 

6 

3      =6 

Philadelphia,  Pa.  .       10,742 

3-75 

5 

Cement  Grout 

6 

3      :6 

Pittsburgh,  Pa  

19,764 

3.18          i 

Bituminous 

6 

3      :6 

Chicago,  111  

40,340 

3-78t 

2 

Pitch 

6 

3      :6 

Duluth,  Minn.  .  .  . 

6,258 

2-75t 

Cement  Grout 

5 

3      :6 

San  Francisco,  Cal. 

22,049 

3-28    |    .. 

Asphalt 

6 

2^7 

*  Price  covers  pavement,  foundation,  and  shaping  subgrade. 
t  Does  not  include  shaping  subgrade. 


STONE  TRACKWAYS.       Trackways  have  been  built,  both  in 
this  country  and  abroad,  of  stone  slabs,  brick,  concrete  blocks, 


FIG.  161.     Stone  Trackway  in  Glasgow,  Scotland. 

steel  shapes,  and  other  materials.  Stone  trackways  were  used 
on  one  of  the  old  toll  roads  in  New  York  State  as  early  as  1831. 
The  slabs,  which  measured  24  inches  in  width  by  4  inches  in 
thickness,  were  laid  with  a  gauge  which  would  accommodate 
the  vehicles.  The  space  between  them  was  paved  with  cobble- 


372  ELEMENTS    OF   HIGHWAY    ENGINEERING 

stone.  Trackways  of  rectangular  stone  blocks,  averaging  12 
inches  wide,  6  inches  thick,  and  of  varying  lengths,  have  been 
used  in  some  cities  of  England  and  Scotland  on  steep  hills  cr 
where  the  traffic  is  exceptionally  heavy.  Fig.  161  shows  one  of 
these  trackways  on  a  street  in  Glasgow.  Granite  trackways, 
made  of  slabs  2  feet  wide,  i  foot  thick,  spaced  4  feet  apart  on 
centers,  are  used  in  several  cities  in  Switzerland. 

COBBLESTONE     PAVEMENTS.      Cobblestone    pavements    are 
now  rarely  laid  except  on  unimportant  streets  or  alleys.    Hard, 


FIG.  162.     Cobblestone  Pavement. 

durable  stones  ranging  from  5  to  10  inches  in  depth  and  from 
4  to  8  inches  across  the  head  are  used.  The  stones  are  laid  on 
a  bed  of  loamy  sand  about  six  inches  thick,  and  are  set  com- 
pactly together  so  as  to  break  joints  as  much  as  possible.  The 
surface  is  then  covered  with  sand,  which  is  swept  into  the  joints, 
after  which  the  stones  are  tamped  with  a  rammer  weighing 
about  50  pounds.  When  there  is  no  further  settlement  of  the 
stone,  the  surface  is  covered  with  a  layer  of  sand  about  yi  an 
inch  in  depth.  A  cobblestone  pavement,  if  subjected  to  a  heavy 
traffic,  soon  becomes  very  uneven.  Fig.  162  shows  a  typical 


STONE   BLOCK   PAVEMENTS  373 

cobblestone  pavement.     The  cost  of  this  type  of  pavement  is 
from  60  to  70  cents  per  square  yard. 

CLINKER  AND  SLAG  BLOCK  PAVEMENTS.  About  33  percent 
of  the  total  refuse  of  a  refuse  destructor  remains,  after  burning, 
as  clinker.  Many  experiments  have  been  tried  to  utilize  clinker 
commercially.  It  has  been  ground  and  used  as  sand  and  has 
also  been  broken  up  and  pressed  into  bricks,  paving  blocks  and 


FIG.  163.     Blow-hole  in  Slag  Block. 

slabs,  either  a  cement  or  bituminous  material  being  added  to 
bind  the  fine  particles  together.  These  bricks,  blocks,  and  slabs 
have  been  used  in  building  construction  and  in  pavements  for 
streets  and  sidewalks.  Blocks  manufactured  with  clinker  and  a 
hydraulic  cement  as  a  binder,  in  the  proportions  of  three  parts 
of  clinker  to  one  part  of  cement  and  one  to  eight  parts  of  fine 
dust,  have  not  made  a  very  satisfactory  pavement  in  the  Bor- 
ough of  Finsbury,  England,  when  subjected  to  a  heavy  traffic. 
In  fact,  many  square  yards  of  this  pavement  had  to  be  taken 
up  after  it  had  been  down  for  only  two  years. 

Molded  slag  blocks  have  been  used  in  England  and  the 
United  States  for  the  construction  of  pavements.  The  details 
of  construction  of  slag  block  pavements  are  similar  to  those 
used  in  the  construction  of  stone  block  pavements.  Careful 


374  ELEMENTS   OF   HIGHWAY    ENGINEERING 

culling  of  the  blocks  is  required  in  order  to  reject  those  which 
contain  blow-holes.  (See  Fig.  163.)  These  blow-holes  in  many 
blocks  are  not  visible  on  the  surface  but  are  soon  disclosed 
under  the  action  of  horse-drawn  vehicle  traffic. 

MAINTENANCE 

The  maintenance  of  a  stone  block  pavement,  see  Fig.  164,  if 
properly  constructed,  is  negligible  for  a  few  years.     The  life  of 


FIG.  164.     A  Well  Maintained  Stone  Block  Pavement  on  a  National  Highway 

in  France. 


a  granite  block  pavement  constructed  on  a  concrete  founda- 
tion is  estimated  to  be  about  twenty-five  years.  The  average 
annual  maintenance  cost  of  stone  block  pavements  will  vary 
from  about  2.0  to  o.i  cents  per  square  yard.  When  the  blocks 
become  worn  so  that  the  surface  is  extremely  uneven,  it  is  pos- 
sible to  take  the  blocks  up,  redress  them,  and  relay  them  as  a 
new  pavement.  The  cost  of  relaying  granite  block  paving, 
including  a  concrete  base  and  recutting  blocks,  is  estimated  at 
$2  per  square  yard.  The  cost  is  about  $2.50  per  square  yard 
when  not  more  than  25  percent  of  new  blocks  are  substituted 
for  the  old  ones  which  are  unfit  for  relaying. 


STONE  BLOCK  PAVEMENTS  375 

CHARACTERISTICS.  • 

The  chief  advantage  of  a  stone  block  pavement  is  its  dura- 
bility. Such  a  pavement  if  properly  constructed  is  able  to 
withstand  the  heaviest  kind  of  traffic  and  is  well  adapted  for 
use  on  those  streets  which  are  subjected  to  the  traffic  of  docking 
districts.  A  stone  block  pavement  is  about  the  only  pavement 
which  can  be  used  on  very  steep  grades  and  furnish  a  good 
foothold  for  horses.  There  were  several  instances  where  it  has 
been  used  on  grades  of  n  percent  and  in  one  case  the  grade 
was  about  19  percent.  When  the  stones  are  rounded  off 
from  wear  or  when  a  grout  filler  is  used  the  pavement  may 
be  somewhat  slippery  soon  after  completion,  particularly  when 
it  is  slightly  wet.  The  chief  defect  of  the  average  stone  block 
pavement  is  its  rough  and  noisy  surface.  When  the  blocks 
get  out  of  place  and  the  filler  does  not  protect  the  edges  of 
the  blocks  from  wear,  the  blocks  become  rounded  off  at  the 
joints  and  a  rough  surface  results.  When  in  this  condition 
the  pavement  is  not  sanitary,  since  it  is  hard  to  clean  and  the 
joints  afford  a  place  for  the  collection  of  all  kinds  of  filth. 


CHAPTER  XVIII 
STREET  CLEANING  AND  SNOW  REMOVAL 

STREET  CLEANING 

Public  health,  safety,  and  convenience  require  that  road- 
ways should  be  kept  clean.  The  close  relationship  existing  be- 
tween dust  laying  and  street  cleaning  is  obvious.  On  certain 
types  of  roadways  such  as  earth,  gravel,  and  broken  stone,  the 
problem  is  a  combination  of  cleaning  and  dust  laying.  On 
such  pavements  as  brick,  stone  block,  cement-concrete,  wood 
block,  bituminous  macadam,  bituminous  concrete,  and  sheet 
asphalt,  only  methods  of  cleaning  need  to  be  considered.  In 
the  former  class  after  the  surface  is  cleaned  dust  remains  which 
must  be  treated  to  prevent  its  being  a  nuisance.  In  the  latter 
case  such  efficient  methods  of  cleaning  should  be  employed  as  to 
remove  all  distributable  dust.  The  method  of  cleaning,  there- 
fore, depends  primarily  upon  the  kind  of  roadway.  There  are 
other  factors  which  influence  the  selection  of  the  method,  such 
as  the  character  and  amount  of  traffic,  the  environments  of 
the  highway,  and  other  local  conditions.  A  general  description 
of  the  various  methods  in  use  in  the  United  States  is  presented, 
followed  by  a  discussion  of  methods  applicable  to  each  of  the 
several  types  of  roads  and  pavements  and  brief  references  to 
American  and  European  practice. 

HAND  CLEANING.  Hand  cleaning  is  done  either  by  gangs  or 
patrols,  usually  during  the  daytime.  In  the  first-named  method 
the  roadway  is  cleaned  at  frequent  intervals,  while  in  the  latter 
case  a  patrolman  has  a  certain  district  to  clean  each  day.  Each 
patrolman  has  a  push  broom,  shovel,  and  can  or  bag  carrier  in 
which  to  collect  the  refuse.  The  principal  disadvantage  of  the 
gang  method  is  that  the  streets  are  in  an  objectionable  condi- 
tion for  the  greater  part  of  the  interval  between  consecutive 
cleaning  operations.  In  the  patrol  system  the  material  is  col- 

376 


STREET   CLEANING  AND    SNOW   REMOVAL 


377 


lected  in  cans  or  bags  and  placed  to  one  side  ortis  swept  into 
heaps  at  the  side  of  the  street,  each  awaiting  the  arrival  of 
wagons  to  carry  the  refuse  to  the  dumping  grounds.  In  almost 
every  city  in  Europe  may  be  found  a  patrol  system  well  or- 
ganized and  highly  efficient,  but  in  the  United  States  poor 
supervision  and  general  indifference  on  the  part  of  the  public 


Courtesy  of  Mr.  A.  F.  Masury. 

FIG.  165.     Motor  Truck  Pressure  Sprinkler. 

result  in  the  lax  and  shiftless  systems  encountered  in  so  many 
of  our  smaller  cities. 

The  ordinary  push  broom,  about  sixteen  inches  wide,  is  uni- 
versally used  in  street  cleaning  operations.  The  head  is  filled 
with  split  bamboo,  rattan,  hickory,  or  steel  wire.  One  edge  of 
the  broomhead  is  sometimes  fitted  with  a  steel  scraper.  These 
brooms  are  used  for  heavy  sweeping.  For  lighter  and  more 
thorough  sweeping  the  head  is  filled  with  bass  wood,  which  is 
more  pliable  than  some  of  the  other  forms  of  filling.  In  Europe 
hand  brooms  made  out  of  birch  or  other  twigs  are  still  used 


378  ELEMENTS   OF   HIGHWAY   ENGINEERING 

to  some  extent  for  light  sweeping.  Sweepings  may  be  collected 
in  galvanized  iron  cans  or  in  bags  which  are  later  removed  by 
wagons.  Cans  for  holding  sweepings  are  fixed  to  a  wheel  truck 
in  such  a  manner  that  they  can  be  attached  and  detached  from 
the  truck  by  a  very  simple  operation.  A  dust  pan  is  also  attached, 
into  which  the  sweepings  are  broomed. 

MACHINE    SWEEPING.      Horse    sweepers    are    employed   in 
many  cases,   the  work  being  done  generally  at  night.     Such 


Courtesy  of  Charles  Hvass  and  Co. 

FIG.  1 66.     Rotary  Sweeper  and  Sprinkler. 

sweeping  should  always  be  preceded  by  sprinkling  to  ensure  the 
laying  of  the  dust.  Horse-drawn  sprinklers  have  been  previously 
described  in  Chapter  V.  Motor  truck  sprinklers,  as  shown  in 
Fig.  165,  some  of  which  have  the  sprinkling  attachment  on  the 
front  of  the  machine  instead  of  in  the  rear,  are  used  in  Europe 
and,  to  a  limited  extent,  in  the  United  States.  There  are  numer- 
ous combined  sweepers  and  sprinklers,  both  horse-drawn  and 
motor-propelled,  in  use  in  Europe  and  a  few  cities  of  the  United 
States.  This  treatment  alone  is  efficient  on  streets  subjected  to 
light  traffic,  but  on  the  heavier  travelled  thoroughfares  it  should  be 
supplemented  by  hand  sweeping  during  the  day.  A  pavement  in 


STREET   CLEANING  AND    SNOW   REMOVAL  379 

good  repair  is  essential  for  best  results  with  a  mechanical 
sweeper. 

Rotary  horse-drawn  sweepers,  see  Fig.  166,  are  made  to 
sweep  widths  varying  from  6  to  9  feet.  By  means  of  levers 
operated  by  the  driver  the  broom  can  be  made  to  engage  the 
road  surface  with  either  a  light  or  heavy  pressure.  The  brooms 
are  filled  with  rattan,  split  bamboo,  or  hickory.  Several  types 
of  pick-up  sweepers  have  been  designed  and  used.  One  of  the 
most  successful  is  pushed  by  hand  and  consists  of  a  rotary 
brush  geared  to  the  wheels.  The  brush  is  covered  in  with  a 
hood  and  operates  on  the  carpet  sweeper  principle,  throwing  the 
sweepings  into  a  pan  which  is  a  part  of  the  machine.  The 
sweeper  will  clean  at  one  passage  a  strip  30  inches  wide.  Motor 
pick-up  sweepers,  which  have  been  used  in  Europe,  as  a  rule 
have  been  found  to  give  satisfactory  results,  although  the  cost 
of  operation  has  not  been  accurately  estimated.  These  machines 
are  generally  provided  with  a  water  tank  which  sprays  the  dust 
just  before  it  is  picked  up. 

HOSE  FLUSHING.  Hose  flushing  is  employed  to  a  consider- 
able extent  in  Europe  and  to  a  limited  extent  in  this  country. 
Flushing  is  accomplished  by  applying  a  stream  of  water  to  the 
surface  with  a  broad,  sweeping  motion.  In  addition  the  pave- 
ment is  scrubbed  with  rubber  squeegees  worked  by  hand  to 
remove  any  adhering  solid  matter.  The  squeegees  are  made  of 
wood  or  metal  with  a  rubber  edge  varying  from  12  to  20  inches 
in  width.  The  material  is  carried  in  suspension  to  the  sewer 
through  the  nearest  catch-basin.  This  treatment  is  particularly 
efficacious  in  removing  all  fine  dirt,  but  it  necessitates  the  pre- 
liminary removal  of  all  coarse  material  which  otherwise  would 
eventually  clog  the  average  sewer. 

MACHINE  SCRUBBING  AND  FLUSHING.  Sprinkling  combined 
with  the  use  of  a  rotary  scrubber  or  squeegee  is  satisfactorily 
used  on  smooth  pavements  for  the  removal  of  dust.  Some 
machines  are  equipped  with  attachments  for  sprinkling  the  pave- 
ment just  in  advance  of  a  rotary  squeegee.  (See  Fig.  167.)  There 
are  also  various  types  of  flushing  machines  used  on  sheet  and 
block  pavements  which  throw  the  water  in  broad,  fan-shaped 


380 


ELEMENTS    OF   HIGHWAY    ENGINEERING 


sprays  over  the  surface,  thus  washing  the  dirt  into  the  gutters 
and  eventually  into  the  sewers.     (See  Fig.  168.) 

METHODS  APPLICABLE  TO  VARIOUS  TYPES  OF  ROADS  AND 
PAVEMENTS  IN  URBAN  DISTRICTS.  Earth,  gravel,  and  broken 
stone  roadways  are  cleaned  by  gangs  or  patrolmen  with  push 


Courtesy  of  Charles  Hvass  and  Co. 


FIG.  167.     Rotary  Squeegee. 

brooms  or  by  horse-drawn  or  motor-driven  rotary  sweepers. 
Bituminous  surfaces,  and  good  brick,  bituminous  and  wood 
block  pavements  are  cleaned  of  coarse  dirt  by  gangs  or 
patrolmen  during  the  day  and  by  hose  flushing  and  squeegee- 
ing or  by  rotary  scrubbers  or  squeegees  during  the  night.  Brick, 
in  poor  condition,  and  stone  block  pavements  are  cleaned 
during  the  day  by  gangs  or  patrolmen  and  during  the  night 
with  rotary  brushes  and  hand  or  machine  flushing  methods. 
In  all  the  methods  the  dirt  is  forced  to  the  gutters  and  is  usually 
removed  by  gangs  with  wagons  following  the  machines. 

NEW  YORK.      The  cleaning  is  done  under  the  direction  of 
the  Department  of  Street  Cleaning.     The  streets  are  cleaned 


STREET  CLEANING  AND   SNOW   REMOVAL  381 

mainly  by  hand  sweeping,  the  laborers  working  under  the 
patrol  system.  Each  laborer  is  supplied  with  a  can  carrier,  a 
push  broom,  and  short  handled  broom,  a  long  handled  scraper 
and  a  dust  pan.  Each  patrolman  has  a  certain  definite  area 
that  he  must  keep  clean,  the  length  varying  from  a  few  hundred 
feet  to  one  mile,  depending  upon  the  type  of  pavement  and  the 
traffic.  Most  of  the  hand  sweeping  is  accomplished  in  the  day- 


CourUsy  of  Mr.  A .  F.  Masury. 

FIG.  1 68.     Motor  Truck  Flushing  Machine. 

time  without  previous  sprinkling.  Horse-drawn  sweepers  and 
squeegees  are  employed  to  a  limited  extent,  the  work  being  done 
mostly  at  night.  During  the  daytime,  in  the  summer  months, 
a  few  streets  of  the  city  in  the  crowded  districts  are  flushed, 
either  by  hose  or  by  machine. 

PHILADELPHIA.  Broken  stone  roads  are  cleaned  by  brushing 
coarse  dirt  into  the  gutters,  once  a  week,  once  in  two  weeks, 
or  once  a  month,  dependent  upon  traffic  and  location.  Pave- 
ments are  cleaned  every  day,  every  other  day,  every  third  day, 
or  once  a  week,  dependent  upon  traffic,  location,  and  other  local 
conditions.  Smooth  bituminous  pavements,  brick  pavements  in 


382  ELEMENTS    OF  HIGHWAY   ENGINEERING 

good  condition,  and  wood  block  pavements  are  cleaned  by  patrol- 
men with  brooms  and  with  rotary  squeegees.  Wavy  bituminous 
pavements,  brick  pavements  in  poor  condition,  and  stone  block 
pavements  are  hand  and  machine  broomed  and  cleansed  with 
power  flushers. 

BOSTON.  The  business  streets  are  swept  by  machine  sweepers 
each  day,  shortly  after  midnight.  The  streets  are  then  flushed 
with  flushing  machines.  During  the  daytime  the  streets  are 
kept  clean  by  hand  patrol. 

WASHINGTON,  D.  C.  The  work  is  under  the  supervision 
of  the  Division  of  Street  Cleaning,  which  is  a  part  of  the  engi- 
neering department  of  the  District.  All  of  the  streets  in  the 
central  portion  of  the  city  are  cleaned  by  hand  patrol  each 
day,  with  the  exception  of  Sundays  and  holidays.  In  this  work 
each  street  is  actually  swept  over  about  three  times.  The  streets 
outside  of  the  section  which  is  cleaned  by  hand  patrol  are 
sprinkled  and  swept  by  machine  sweepers  about  three  times  a 
week.  Alleys  are  cleaned  about  once  a  week,  and  unpaved 
streets  are  cleaned  about  once  every  ten  days.  The  streets  in 
the  central  portion  of  the  city,  besides  being  cleaned  by  hand 
patrol,  are  sprinkled  and  gone  over  with  a  rotary  squeegee 
about  three  times  in  two  weeks.  The  streets  in  the  hand  patrol 
section  are  paved  largely  with  sheet  asphalt  and  asphalt  block. 
The  streets  which  are  paved  with  stone  block  or  cobble  are 
cleaned  with  pressure  flushing  machines. 

GREAT  BRITAIN.  Yabbicom  *  has  described  the  methods  of 
street  cleaning  typical  of  twenty  towns  of  England,  including 
five  of  the  boroughs  of  the  City  of  London,  and  fifteen 
towns  outside  of  the  great  metropolis,  including  such  cities  as 
Liverpool,  Manchester,  Edinburgh,  and  Belfast.  He  found  that 
32  percent  of  the  streets  in  sixteen  of  these  towns  are  paved 
with  stone  setts,  3  percent  with  wood  paving,  5  percent  with 
various  materials,  including  asphalt,  and  60  percent  with  broken 
stone.  The  principal  streets  in  all  of  the  towns  are  cleaned 
at  least  once  each  day,  and  more  frequently  when  necessary. 
The  second-class  streets  are  swept  three  times  a  week,  while 

*  Report  No.  34,  Second  International  Road  Congress,  Brussels,  1910. 


STREET   CLEANING   AND    SNOW    REMOVAL  383 

the  suburban  roads  are  cleaned  in  some  places  only  once  a 
week.  The  streets  are  swept  during  the  night  in*  eight  towns, 
during  the  day  in  seven,  and  during  both  day  and  night  in  five. 
Street  orderlies,  mostly  boys,  are  employed  during  the  daytime 
in  each  town  to  pick  up  the  litter  and  sweep  up  horse  droppings. 
The  refuse  gathered  by  the  street  orderlies  is  placed  in  small 
hand-carts  and  dumped  at  some  depot,  or  it  is  placed  in  bins 
which  are  constructed  above  or  below  the  level  of  the  pave- 
ment. Street  sweeping  is  generally  preceded  by  sprinkling  when 
the  streets  are  dry.  Motor  vehicles,  as  well  as  those  drawn  by 
horses,  are  used  for  watering  in  Westminster  and  Cardiff.  Records 
from  twenty  towns  showed  that  horse-drawn  sweepers  are  used 
in  fourteen  to  clean  the  broken  stone  roads. 

In  London  the  street  cleaning  is  done  under  the  direction  of 
the  Engineering  Bureau  of  the  Public  Health  Department.  Each 
night  the  streets  of  the  city  are  washed  by  hose  flushing  or  by 
water-carts,  the  work  being  done  between  the  hours  of  8  P.M. 
and  6  A.M.  Men  broom  or  squeegee  the  surface  during  the 
process  of  washing.  During  the  daytime  the  streets  are  swept 
by  hand  with  brooms  in  dry  weather  and  squeegeed  in  wet 
weather.  The  streets  are  also  patrolled  by  "orderly"  boys. 

FRANCE.  In  Paris  the  street  cleaning  is  done  under  the 
direction  of  the  Department  of  Public  Works.  Between  4  A.M. 
and  7  A.M.  many  streets  are  watered  and  then  swept  with  horse- 
drawn  sweepers  and  the  sidewalks  are  swept  with  hand  brooms. 
The  refuse  is  either  swept  to  the  gutters  or  collected  and  placed 
in  pits  and  removed  by  carts.  During  the  day  some  streets  are 
swept  with  hand  brooms,  the  material  being  brushed  into  the 
gutters,  where  it  is  carried  away  to  the  sewers  by  water  flushing. 
Horse-drawn  squeegees  are  employed  for  cleaning  asphalt  and 
wood  pavements. 

GERMANY.  In  Berlin  a  special  committee  of  the  City 
Council  has  charge  of  the  street  cleaning  operations.  Rotary 
machine  brooms  are  used  to  sweep  the  streets  at  night,  begin- 
ning at  11.30  P.M.  During  the  day  the  streets  are  sprinkled 
by  motor  wagons  and  horse-drawn  carts.  Watering  is  imme- 
diately followed  by  cleaning  with  horse-drawn  and  motor-driven 


384  ELEMENTS   OF   HIGHWAY   ENGINEERING 

rotary  squeegees.  In  those  places  where  the  water  is  not  re- 
moved by  the  machine  squeegees,  the  pavements  are  cleaned 
by  men  or  boys  with  hand  brooms  or  squeegees.  Although 
several  machines  which  dampen,  sweep,  and  take  up  the  mate- 
rial have  been  used,  they  have  not  proved  to  be  very  satisfactory. 

SNOW  REMOVAL 

The  methods  used  in  dealing  with  snow  on  highways  are 
influenced  to  a  great  extent  by  climatic  conditions.  There  are 
localities  in  northern  climates  or  in  high  altitudes  where  the 
snowfall  is  heavy  and  the  cold  is  so  intense  and  constant 
that  the  snow  does  not  melt  appreciably  until  spring.  In 
such  places  it  is  not  so  much  a  question  of  removing  the 
snow  as  it  is  of  making  the  highways  passable.  The  drifts  are 
cut  through  or  smoothed  out  and  the  whole  roadway  is  com- 
pacted by  a  light  roller. 

In  practically  all  of  the  large  cities  of  the  United  States, 
and  many  of  those  of  Europe,  it  is  the  practice  to  remove  the 
snow  from  the  business  districts  as  soon  as  possible.  If  not 
efficiently  removed  a  heavy  snowfall  will  not  only  cause  extreme 
inconvenience  to  the  public,  but  it  may  seriously  impede  and 
hinder  the  traffic  and  business  of  a  city. 

A  great  deal  of  attention  is  given  in  European  cities  to 
planning  a  scheme  of  organization  early  in  the  season  to  per- 
form the  work  of  removing  the  snow,  so  that  it  may  be 
accomplished  without  any  unnecessary  delays.  Many  times 
district  depots  are  established  with  an  equipment  of  tools 
and  implements  sufficient  to  do  the  work  in  that  district. 
Laborers  are  hired  with  the  understanding  that  when  the  snow 
commences  to  fall  they  are  to  report  to  a  particular  station 
for  work.  The  work  can  be  efficiently  attacked  in  this  way, 
as  the  superintendent  of  the  district  knows  beforehand  just 
what  means  he  will  have  at  hand  to  carry  it  out.  In  many 
places  both  in  Europe  and  in  this  country,  it  is  customary  to 
let  out  the  work  of  snow  removal  by  contract.  The  method 
for  paying  for  contract  work  varies  in  different  communities. 
In  some  places  the  area  of  the  roadway  surface  is  determined 


STREET  CLEANING  AND   SNOW  REMOVAL 


385 


and  a  price  agreed  upon  for  each  inch  of  thickness  of  snow, 
including  the  cost  of  sweeping  and  transporting  to  the  dumping 
place.  Another  method  is  to  obtain  a  price  per  cubic  yard  of 
snow  swept  and  heaped  along  the  road  and  a  separate  price  for 
the  transportation.  Some  times  an  overhaul  clause  is  in- 
cluded in  the  contracts. 

REMOVAL  BY   MACHINES.     In  cleaning  the  roadways  with 
machines,  the  snow  is  pushed  towards  the  gutters.     The  snow 


FIG.  169.     Large  Snow  Drifts  at  Curbs. 

from  the  sidewalks  is  also  moved  to  the  same  point,  with  the 
result  that  a  drift  is  formed.  These  drifts  will  assume  large 
proportions  when  a  heavy  snowfall  occurs  and  will  not  only 
restrict  the  limit  of  traveled  way,  but  also  hinder  the  surface 
drainage.  (See  Fig.  169.)  When  the  snow  starts  to  melt  the 
water  will  back  up  into  the  cellars  of  the  abutting  property 
unless  considerable  care  is  taken  to  keep  a  passage  clear  for 
the  water  to  flow  to  the  catch-basins  or  other  inlets.  The  re- 
moval of  the  snow  which  has  been  thus  gathered  is  accom- 
plished in  several  ways.  In  light  storms  the  drifts  are  gathered 
into  large  separate  piles  which  are  later  removed  by  wagons. 
When  the  drifts  are  large  they  are  removed  by  wagons  without 
previous  piling.  The  snow  is  taken  by  the  wagon  to  some 


386 


ELEMENTS    OF   HIGHWAY  ENGINEERING 


natural  waterway,  or  is  dumped  on  vacant  lots,  or  discharged 
through  manholes  into  the  sewers  under  certain  conditions. 
Although  various  machines  have  been  devised  for  the  purpose 
of  melting  the  snow  gathered  together  in  this  manner,  none  of  them 
have  been  successful,  at  least  from  an  economical  standpoint. 


Courtesy  of  Mr.  William  H.  Connell. 

FIG.  170.     Snow  Plow  Attached  to  a  Motor  Truck. 

Removal  by  Plows.  As  a  general  rule  the  streets  on  which 
car  tracks  are  located  are  cleaned  first.  Various  types  of  plows, 
see  Figs.  170  and  171,  are  used  for  this  purpose  in  several 
American  cities.  The  traction  companies  naturally  try  to  keep 
the  cars  moving  and  the  snow  no  sooner  begins  to  fall  than 
special  cars,  equipped  with  brushes  or  plows,  are  sent  over 
the  different  lines  to  clear  the  tracks.  It  is  this  principle  of 
starting  work  of  removal  before  the  snow  attains  any  depth 
that  makes  their  efforts  so  uniformly  successful.  It  is  a  rare 
occurrence  for  the  cars  to  be  blocked  for  any  length  of  time 
except  in  the  most  severe  storms.  The  work  done  by  the 
traction  companies  is  of  the  utmost  assistance  to  vehicular 


STREET   CLEANING  AND    SNOW   REMOVAL  387 

traffic.  In  many  of  our  American  cities,  after  SL  heavy  fall 
of  snow,  the  cleared  trackway  is  the  only  place  which  is 
accessible  for  vehicular  traffic.  In  Vienna  the  tramways  are 
controlled  by  the  municipality,  and  it  is  the  practice  there  to 
plow  the  snow  from  the  roadway  toward  the  gutter  at  the 


Courtesy  of  the  Mercury  Mfg.  Co. 

FIG.  171.     Motor  Tractor  Snow  Plow. 

same  time  it  is  removed  from  the  trackway.  This  is  accom- 
plished by  coupling  two  plows  to  the  car.  The  plows  con- 
sist of  platforms  mounted  on  four  wheels,  underneath  which 
are  a  series  of  horizontal  rods  to  which  are  attached  vertical 
blades  capable  of  being  raised  or  lowered.  When  the  plows 
are  used  in  pairs,  one  is  drawn  at  one  side  and  just  behind  the 
other  in  such  a  way  as  to  clear  two  widths  at  one  passage. 
Ordinary  V-shaped  plows  are  used  extensively  to  clear  a  path 
for  vehicles  on  highways  not  occupied  by  car  tracks. 

Removal  by  Sweepers.  Rotary  brushes  can  be  successfully 
used  to  remove  light  falls  of  snow.  In  Paris  these  sweepers  are 
used  for  snowfalls  from  ^  to  i  inch  in  thickness.  Rotary 
brushes  are  also  used  by  the  traction  companies  in  clearing 
snow  from  the  tracks,  in  which  case  the  brush  is  generally  run 


388  ELEMENTS   OF   HIGHWAY   ENGINEERING 

by  a  motor.  One  objection  to  horse-drawn  sweepers  for  snow 
removal  is  that  the  speed  of  the  brush  is  not  fast  enough  to 
prevent  the  bristles  from  becoming  choked  up  with  snow.  Road 
scrapers  can  be  used  sometimes  very  advantageously  in  doing 
this  work.  (See  Fig.  172.) 

REMOVAL  BY  USE  OF  SALT.     The  use  of  salt  in  connection 


Courtesy  of  Mr.  William  H.  Connell. 

FIG.  172.     Road  Scrapers  Used  to  Remove  Snow. 

with  snow  removal  is  objected  to  by  some  on  account  of  the 
intense  cold  produced  and  its  injurious  effects  on  shoe  leather 
and  horses'  hoofs.  In  Paris,  however,  as  soon  as  the  snowfall 
occurs,  the  workmen  commence  at  once  to  spread  rock  salt  on 
the  roadways.  The  salt  produces  a  thawing  action  after  the 
traffic  has  mixed  it  with  the  snow.  The  mixture  of  snow  and 
salt  is  then  swept  to  the  gutters  by  sweeping  machines,  after 
which  it  is  flushed  into  the  sewers. 

REMOVAL  BY  FLUSHING.  The  practice  of  flushing  is  quite 
common  in  many  European  cities.  Flushing  is  not  carried  on 
when  the  temperature  is  below  the  freezing  point  on  account 
of  the  danger  of  ice  forming  in  the  sewers. 


CHAPTER  XIX 
COMPARISON  OF  ROADS  AND  PAVEMENTS 

The  determination  of  the  most  economical  and  efficient 
method  of  construction  and  maintenance  to  be  employed  on 
different  highways  constitutes  one  of  the  most  important  sub- 
jects which  the  highway  engineer  has  to  consider.  The  solution 
of  the  problem  depends  upon  many  variable  factors,  all  of  which 
must  be  given  due  consideration  and  the  proper  value  attached 
to  each.  The  great  variety  of  materials  and  methods  of  con- 
struction and  maintenance  used,  together  with  the  absence  of 
such  essential  information  as  traffic  censi,  cost  data,  etc.,  makes 
it  a  difficult  matter  to  reduce,  for  a  given  location,  all  of  the 
different  types  of  roads  and  pavements  to  a  comparable  basis. 

DEVELOPMENT.  The  small  amount  of  scientific  comparison 
of  roads  and  pavements  which  has  been  undertaken  in  the  United 
States  is  attributable  to  many  causes,  among  which  may  be 
noted  the  following: 

First.  Political  interference  in  the  selection  of  the  men  placed 
in  control  of  highway  work,  and  with  the  work  of  design,  con- 
struction, and  maintenance  of  roads  and  streets,  and  the  inter- 
ference by  controlling  bodies  of  laymen  in  the  legitimate  work 
of  the  highway  engineer. 

Second.  The  continual  change  in  the  personnel  of  the  engi- 
neering staff  in  control  of  highway  work. 

Third.  Division  of  responsibility  in  the  supervision  of  high- 
way work,  particularly  in  municipalities,  but  also  applicable  in 
some  states,  as,  for  instance,  those  in  which  the  state  depart- 
ment supervises  the  design  and  construction,  while  the  respon- 
sibility for  maintenance  is  placed  upon  the  county  or  town. 

Fourth.  The  search  by  many  officials  for  a  panacea  for  the 
treatment  of  all  classes  of  roads  and  streets. 

Fifth.  The  comparatively  small  number  of  well-trained  high- 

389 


390  ELEMENTS   OF  HIGHWAY   ENGINEERING 

way  engineers  who  have  devoted  the  requisite  time  and  energy 
to  the  problems  of  economics,  administration,  organization, 
construction,  and  maintenance  connected  with  highway 
engineering. 

Sixth.  The  comparatively  infinitesimal  amount  of  investiga- 
tion which  has  been  considered  necessary  as  preliminary  to  the 
design  of  a  road  or  street  or  a  system  of  highways. 

Seventh.  A  confusion  of  ideas  on  the  part  of  many  as  to  the 
reasons  for  the  success  or  failure  of  a  given  road  or  pavement. 

ESSENTIALS  OF  AN  IDEAL  ROAD  OR  PAVEMENT.  An  ideal 
road  or  pavement  should  be  durable,  noiseless,  suitable  for  users, 
easily  cleaned  and  made  dustless,  non-slippery  for  horses  and  all 
classes  of  vehicles  under  varying  climatic  conditions,  easily  main- 
tained, should  yield  neither  dust  nor  mud,  have  a  low  tractive 
resistance,  low  first  cost,  low  annual  cost,  low  maintenance 
charge,  and  an  aesthetic  and  impervious  surface. 

A  consideration  of  these  important  characteristics  reveals 
the  lack  of  accurate  data  which  are  available  relative  to  each. 
However,  certain  information  is  at  hand  which  materially  aids 
in  a  comparison  of  roads  and  pavements  from  different  stand- 
points. 

Durability.  The  life  of  a  road  or  pavement  is  expressed 
either  in  terms  of  (a)  the  number  of  years  during  which  it  can 
be  maintained  in  a  satisfactory  condition  at  a  cost  per  year 
which  has  not  reached  an  amount  so  that  reconstruction  is 
economical  or,  (b)  the  total  number  of  tons  per  yard  or  foot 
of  width  that  the  road  or  pavement  is  subjected  to  during  its 
life.  As  durability  is  a  function  of  a  number  of  variables  among 
which  the  amount  of  traffic  is  of  primary  importance,  method 
(b)  usually  conveys  more  information  than  the  first  method. 

In  employing  method  (a),  based  on  practice  in  central 
western  cities,*  the  following  average  values  for  "life"  have 
been  assigned  to  several  types  of  roads  and  pavements.  In  each 
case  the  estimated  life  is  based  on  the  supposition  that  the  road 

*  Hugh  J.  Fixmer,  Division  Engineer,  Chicago  Board  of  Local  Improve- 
ments, in  1915  Proceedings  Illinois  Society  of  Engineers  and  Surveyors, 
pages  55-56. 


COMPARISON   OF    ROADS   AND   PAVEMENTS 


391 


or  pavement  is  used  under  suitable  local  conditions  as  indicated 
in  the  second  column. 


Type  of  Road  or  Pavement 

Suitable  Street 

Life  in 
Years 

Oranite  block 

Heavy  traffic 

T.Q 

Creosoted  wood  block  

Business  

I5-2O 

Brick 

Car  line    

2O 

Sheet  asphalt  
Asphaltic  concrete  

Residential  
Residential  and  boulevards  . 
Light  traffic 

16 

12-20 

6—  10 

Light  traffic 

8 

Broken  stone 

Light  traffic 

A 

Method  (b)  is  employed  by  John  A.  Brodie,  City  Engineer 
of  Liverpool,  in  a  comparison  of  the  tonnage  life  of  different 
kinds  of  stone  block  pavements  and  broken  stone  roads. 

"Taking  heavy  traffic  streets  first,  experience  shows  that  accu- 
rately dressed  setts — 6  inches  deep  by  6  inches  to  8  inches  long 
by  4  inches  wide,  laid  on  a  sound  concrete  foundation,  at  least 
8  inches  deep,  with  a  small  sand  bed  between  the  underside  of 
the  sett  and  the  concrete,  the  joints  being  thoroughly  racked 
with  hard  shingle  and  afterwards  grouted  with  a  permanent 
pitch  mixture,  which  prevents  any  movement  in  the  stones,  and 
renders  the  whole  surface  perfectly  impervious  to  weather- 
give  a  life  equal  to  at  least  seven  and  one-half  million  tons  per 
yard  width,  and  under  these  conditions  this  life  has  often  been 
exceeded. 

"It  is  at  present  impossible  to  say  whether  an  equal  tonnage- 
life  can  be  obtained  from  the  similar  shallower  4-inch  class  of 
construction  in  streets  taking,  say,  60,000  tons  per  yard  of 
width,  as  this  would  mean  a  life  exceeding  100  years;  but  ex- 
perience shows  that  the  total  average  wear  of  the  setts  has  been 
exceedingly  small,  and  it  is  a  fact  that  many  such  streets  exist 
in  Liverpool  to-day,  having  a  life  of  from  25  to  30  years  without 
requiring  any  important  repairs  during  that  time  due  to  wear 
of  the  material. 

"When  the  same  quality  of  stone  is  used  in  ordinary  macadam 
laid  6  inches  to  7  inches  deep  on  a  sound,  hand-packed  founda- 
tion, experience  shows  that  the  tonnage-life  of  the  surface  before 


392  ELEMENTS   OF  HIGHWAY   ENGINEERING 

requiring  to  be  recoated  is  enormously  decreased,  and  instead  of 
seven  and  one-half  millions,  a  figure  about  100,000  tons  only,  or 
about  75  times  less  than  the  result  for  setts  previously  given, 
has  been  obtained  on  a  street  of  moderate  traffic — a  somewhat 
startling  difference." 

Sanitary  Qualities.  The  sanitariness  of  a  road  or  pavement 
is  based  on  its  imperviousness,  smoothness,  and  freedom  from 
dust  and  mud.  From  the  standpoint  of  the  public  health, 
noiselessness  might  properly  be  considered  under  this  head,  as 
it  affects  the  health  of  nervous  people. 

The  several  roads  and  pavements  may  be  classified  as  follows, 
the  groups  being  given  in  the  order  of  their  desirable  sanitary 
properties:  first  group,  sheet  asphalt,  bituminous  concrete, 
cement-concrete;  second  group,  creosoted  wood  block,  bitumi- 
nous macadam,  bituminous  surface,  stone  block  and  brick,  with 
well-filled  joints;  third  group,  broken  stone,  gravel,  earth,  stone 
block  and  brick,  with  open  joints. 

Noiselessness.*  "A  quiet  pavement  has  become  particularly 
important  at  this  time.  With  the  strenuous  life  of  the  modern 
cities  the  nerves  of  the  workers  must  be  protected,  and  it  is 
the  testimony  of  all  brain  workers  that  noise  is  a  great  dis- 
turber. Constant -complaints  are  coming  to  city  departments 
not  only  of  the  great  disturbance  to  the  nerves  of  the  workers 
but  actual  loss  of  time  in  schools,  offices,  and  court  rooms,  and 
interruptions  in  churches  on  account  of  the  noise  over  rough 
pavements.  Hospitals  all  complain  of  the  noise  on  account  of 
the  damage  done  to  patients. 

"  Of  the  different  kinds  of  pavements  herein  stated,  one  of 
wood  blocks  is  least  noisy,  followed  by  asphalt,  asphalt  block, 
bitulithic,  brick,  and  granite  as  the  most  noisy.  It  often  hap- 
pens, however,  that  on  account  of  grades  or  extremely  heavy 
traffic  it  is  necessary  to  lay  granite  even  where  a  quiet  pave- 
ment is  desired.  In  this  case  special  care  must  be  used  to 
reduce  the  amount  of  noise  to  a  minimum.'7 

Slipperiness.  The  comparison  of  pavements  from  the  stand- 
point of  slipperiness  has  naturally  been  confined  by  early  investi- 

*  George  W.  Tillson  in  Engineering  and  Contracting,  October  18,  1911. 


COMPARISON   OF   ROADS   AND   PAVEMENTS  393 

gators  to  the  effect  on  horses.  It  is  evident  that  future  investiga- 
tions along  this  line  should  include  consideration  of  slipperiness 
for  all  classes  of  vehicles  under  varying  climatic  conditions. 
From  the  former  viewpoint,  that  is,  with  reference  to  horses, 
stone  block  with  joints  filled  with  a  bituminous  filler  ranks  first 
as  a  non-slippery  pavement.  Hillside  vitrified  brick  or  ordinary 
vitrified  block  constructed  with  a  bituminous  filler  is  adaptable 
for  steep  grades.  The  other  pavements  and  roads  rank  in  the 
following  order  as  non-slippery;  gravel,  broken  stone,  bitumi- 
nous concrete,  stone  block,  and  brick  with  cement  grouted  joints, 
bituminous  macadam,  bituminous  surfaces,  sheet  asphalt,  and 
wood  block.  The  table  gives  a  general  idea  relative  to  the 
maximum  grades  on  which  it  is  permissible  to  use  different  types 
of  roads  and  pavements. 

Granite  block   pavement    with    bituminous  filled 

joints 1 5  to  20% 

Brick  pavement  with  bituminous  filled  joints 10  to  15% 

Earth  road 10% 

Gravel  road 7  to  10% 

Broken  stone  road 7  to  10% 

Bituminous  concrete  pavement 5  to    8  % 

Stone    block    and    brick    pavements   with   cement 

grouted  joints 5% 

Bituminous  macadam  pavement 3  to    5% 

Cement-concrete  pavement 3  to    5% 

Broken  stone  road  with  bituminous  surface 3  to    5% 

Sheet  asphalt  pavement 3  to    4% 

Wood  block  pavement 2  to    3% 

Haywood  Report.  In  1873  William  Haywood  submitted  a 
report  to  the  Sewer  Commissioners  of  London  which  included  a 
comprehensive  comparison  of  rock  asphalt,  granite  block,  and 
wood  block  pavements  from  the  standpoint  of  relative  slipperi- 
ness. As  a  description  of  methods  of  investigating  slipperiness 
the  report  is  of  interest  to  American  engineers,  but  the  conclu- 
sions stated  cannot  be  used  to  advantage,  as  one  of  the  types 
of  construction,  rock  asphalt,  is  not  in  common  use  in  America. 
Mr.  Haywood's  reports  are  included  in  the  United  States  Special 
Consular  Reports  entitled  "Streets  and  Highways  in  Foreign 
Countries." 

Resistance  to  Traffic.  The  tractive  force  required  to  draw 
vehicles  over  a  given  type  of  road  or  pavement  is  of  importance 


394  ELEMENTS    OF   HIGHWAY   ENGINEERING 

as  a  factor  in  the  selection  of  the  wearing  surface.  Naturally, 
the  weight  to  be  attached  to  this  factor  will  depend  to  a  certain 
extent  upon  the  character  of  the  traffic  which  will  use  the  high- 
way. Investigations  have  been  conducted  upon  which  have  been 
based  certain  conclusions  which  may  serve  as  general  guides. 

The  effect  of  grade  and  the  character  of  the  surface  on  trac- 
tive force  based  on  experiments  conducted  with  a  horse-drawn 
dynamometer  wagon  are  covered  in  the  following  conclusions  * : 

"There  are  so  many  variables  that  enter  in  to  affect  the 
draft  of  any  vehicle,  that  it  is  difficult,  in  a  test  made  under 
actual  working  conditions,  to  separate  the  effect  of  any  one  of 
the  many,  for  the  same  reason  it  is  not  safe  to  put  too  much 
confidence  in  the  results  obtained  from  a  limited  number  of 
tests,  or  to  compare  the  results  made  by  different  persons  under 
unlike  conditions  and  at  widely  varying  times.  Some  of  the 
variables  that  are  sure  to  enter  in,  are:  i,  the  team;  2,  the 
driver;  3,  nature  of  surface;  4,  conditions  of  the  surface;  5, 
grade;  6,  width  of  tire;  7,  diameter  of  wheel;  8,  design  and 
condition  of  vehicle ;  9,  magnitude  of  load ;  10,  curves ;  1 1 ,  slopes. 

"The  tests  conducted  under  the  supervision  of  the  writer, 
since  1908,  have  been  run  with  a  traction  dynamometer  wagon. 
The  dynamometer  proper  is  suspended  from  the  bed  of  a  Stude- 
baker  truck  about  midway  between  the  front  and  rear  axles. 
The  pull  is  transmitted  by  the  tongue  directly  to  the  dyna- 
mometer, which  pulls  on  the  rear  axle.  The  draft  is  measured 
by  the  compression  of  two  carefully  calibrated  coil  springs,  and 
is  transmitted  through  gears  to  a  brass  point  which  marks  the 
record  on  sensitized  paper  operated  by  friction  rolls,  but  over  a 
flat  platen. 

"Grades.  Increasing  the  grade  decreases  the  load  that  can 
be  hauled,  in  each  of  three  ways: 

1.  The  required  pull  per  ton  is  increased. 

2.  The  possible  pull  of  the  horse  is  decreased  by  the  effort 
required  for  the  horse  to  raise  his  own  weight  through  the  grade. 

3.  The  effective  pull  of  the  horse  is  diminished  by  a  change 
in  the  angle  of  the  application  of  the  pull. 

*  Prof.  E.  B.  McCormick  in  Southern  Good  Roads,  January,  1913. 


COMPARISON  OF  ROADS  AND  PAVEMENTS 


395 


"  There  are  no  ways  of  overcoming  the  first  two  losses;  the 
third,  however,  can  be  nearly  if  not  entirely  eliminated  by  a 
change  in  the  methods  of  hitching.  A  comparison  of  the  figures 
in  the  following  table  will  show  very  clearly  the  decrease  of  a 
effective  work  with  the  increase  of  grades.  The  first  column 
shows  the  actual  pounds  of  pull  required  to  draw  a  gross  load 
of  5,270  pounds  over  a  dry,  hard  earth  road,  solid,  and  well 
compacted,  no  dust,  and  using  i^-inch  tires.  These  figures  are 
from  a  test  made  at  the  Kansas  State  Agricultural  College  on 
August  12,  1912.  The  third  column  gives  pounds  pull  required 
per  ton  as  figured  from  values  in  the  second  column.  The 
fourth  column  gives  draft  in  pounds  per  ton  as  taken  from 
results  of  tests  on  macadam  roads.  The  fifth  column  shows 
the  possible  pull  of  a  2,800  pound-  team  on  the  different  grades. 
These  figures  assume  that  a  team  can  exert  a  pull  equal  to 
one-third  of  its  -weight  for  a  short  time,  on  the  level,  and  that 
on  grades  the  tractive  effort  of  the  team  decreases  an  amount 
equal  to  the  grade  resistance  due  to  its  weight,  as  calculated  by 
the  formula: 


Where  W  =  Weight  of  Team 

X  =  Tractive  Effort  of  Team 
G  =  Percent  of  Grade 


Percent 
Grade 

5270 

Pounds 

Earth  Road 
per  Ton 

Macadam 
per  Ton 

Possible  Pull  of 
2800  Lb.  Team  for 
a  Short  Period  of 
Time 

0  
I  
2  

3  

4 

263.0 
3I5-7 

368  .4 
421  .  i 
473-9 

100 
120 
140 

160 

1  80 

38 
58 

78 
ii8 

933 
905 

877 
849 
821 

^ 

526.  s 

2OO 

138 

793 

6      . 

S7Q.2 

22O 

765 

8  

631.9 
684.6 

240 
260 

737 
709 

9  

10  

737-3 
790.0 

280 
300 

68  1 
653 

396  ELEMENTS    OF   HIGHWAY   ENGINEERING 

"A  comparison  of  these  figures  will  show  that  the  necessary 
pull  on  a  10  percent  grade,  over  that  on  a  level,  is  200  percent 
for  an  earth  road,  while  the  decrease  in  effective  pull  for  any 
given  team  is  nearly  30  percent,  and  that  for  a  dirt  road  any 
given  team  can  pull  on  a  10  percent  grade  only  two-ninths  of 
the  load  that  it  can  draw  on  the  level. 

"It  must  be  remembered  that  while  a  team  may  exert  an 
effort  equal  to  one-third  (or  even  one-half)  its  weight  for  a 
short  length  of  time,  it  cannot  do  so  for  an  extended  period. 
The  value  in  such  case,  as  given  by  different  authors,  varies 
one-tenth  to  one-fifth  the  weight  of  the  team. 

"It  is  customary  to  state  the  probable  pull  of  a  horse  or 
team  in  terms  of  its  weight.  This,  of  course,  is  not  accurate,  as 
a  well- trained  team  of  2,000  pounds  will  oftentimes  outpull  a 
poorly  trained  team  of  2,600  pounds  or  2,700  pounds." 

Materials.  Based  upon  the  results  obtained  by  various  in- 
vestigators, Professor  McCormick  has  compiled  a  table  to  show 
the  relationship  existing  between  different  wearing  surfaces  and 
the  tractive  force  in  pounds  per  ton.  Only  a  part  of  the  table  is 
given  here. 

Tractive  Force 
Surface  per  Ton 

Earth  packed  and  dry 100 

Earth — muddy 190 

Sand — loose 320 

Gravel — good 51 

Gravel — loose 147 

Macadam — average 46 

Sheet  asphalt 38 

Asphaltic  concrete 40 

Vitrified  brick — new 56 

Wood  block — good 33 

Annual  Cost.  The  relative  economy  of  different  types  of 
roads  and  pavements  can  only  be  ascertained  by  comparing  the 
annual  costs.  The  annual  cost  is  a  combination  of  the  following 
variables :  interest  on  the  initial  cost  of  the  roadway,  the  annual 
maintenance  charge  and  an  annuity  which  will  in  N  years,  the 
so-called  life  of  the  road,  provide  a  fund  equal  to  the  cost  of 
reconstruction.  If  C  =  annual  cost,  A  =  first  cost,  r  =  rate 
of  interest,  7  =  annual  maintenance  charge,  and  x  =  annu- 


COMPARISON   OF   ROADS   AND   PAVEMENTS  397 

ity,     the    annual    cost    may    be    expressed    by  ^  the    formula 

C  =  Ar  +  I  +  x. 

In  the  case  of  types  of  roads  permitting  partial  reconstruction 
every  M  years,  a  second  annuity  y  should  be  included  in  the 
above  formula  to  take  care  of  this  periodical  reconstruction 
through  N  years  or  the  total  life  of  the  road.  In  order  to  make 
a  fair  comparison  of  the  different  methods  the  same  standard 
of  maintenance  should  be  used  in  each  case. 

Although  theoretically  the  pavement  giving  the  lowest  annual 
cost  would  be  the  most  economical  one  to  build,  there  are  other 
financial  considerations  which  sometimes  make  it  necessary  to 
select  some  other  type  of  pavement.  For  instance,  the  amount 
of  money  at  hand  for  the  improvement  may  not  be  sufficient 
to  pay  for  the  first  cost  of  construction  of  a  pavement  which 
would  give  the  lowest  annual  cost.  Again,  a  road  or  pavement 
that  might  be  the  most  economical  would  require  such  frequent 
repairs  as  to  interfere  with  the  traffic  and  business  conducted  on  it. 

From  the  foregoing  discussion  it  is  evident  that  the  annual 
maintenance  charge  (7)  and  the  annuity  (x)  are  the  variable 
factors  to  which  it  is  difficult  to  assign  definite  values  in  many 
cases.  First  cost,  although  varying  to  a  marked  degree  for 
different  classes  of  pavements  in  various  localities,  may  be  as- 
signed definite  values.  The  initial  costs  of  various  roads  and 
pavements  have  been  considered  in  the  preceding  chapters,  and 
hence  will  not  be  repeated  here. 

Maintenance.  Unfortunately  the  standards  of  maintenance 
vary  widely  throughout  this  country.  Hence,  reports  relative 
to  the  cost  of  this  item  as  a  factor  of  annual  cost  are  of  little 
value  except  in  those  cases  where  it  is  known  what  the  highway 
officials  mean  by  the  statement,  "the  road  is  well  maintained." 
The  ideal  maintenance,  which  should  be  striven  for  in  every 
case,  is  a  method  by  which  the  surface  of  the  highway  is  kept 
in  as  good  condition  as  when  accepted  on  the  completion  of 
construction.  It  is  self-evident  that  it  is  only  possible  to  con- 
form to  this  ideal  by  the  adoption  of  the  principle  of  continuous 
maintenance. 


398 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


Annuity.  The  factor,  annuity,  is  a  function  of  the  variable, 
the  life  of  the  road  or  pavement,  which  was  discussed  under  the 
property,  durability,  in  the  first  part  of  the  chapter. 

Example.  As  an  illustration  of  the  application  of  the  formula, 
the  annual  cost  of  a  granite  block  pavement  laid  on  a  6-inch 
concrete  base  will  be  computed.  It  will  be  assumed  that  the 
first  cost  is  $3.50  per  square  yard;  interest,  4  percent;  annual 
maintenance  cost,  2.4  cents;  life,  25  years;  and  at  the  end  of 
this  period  it  will  be  assumed  that  new  blocks  will  be  laid  on 
the  old  concrete  foundation  at  a  cost  of  $2.50  per  square  yard, 
and  that  in  this  manner  the  life  of  the  pavement  is  renewed  for 
another  25  years.  The  annual  cost  for  50  years,  considering 
the  whole  pavement  to  be  renewed  at  the  end  of  that  period, 
will  be  as  follows:  C  =  $3.50  x  0.04  +  0.024  +  0.023  +  0.060  = 
$0.247  for  the  first  25  years,  C  =  $0.187  f°r  the  second  25  years, 
and  the  mean  of  these  gives  C  =  $0.217  average  for  50  years. 

METHODS  OF  COMPARISON.  The  primary  object  of  a  detailed 
comparison  of  the  relative  merits  of  various  roads  and  pavements 
is  to  enable  the  engineer  to  determine  within  certain  limits  the 
method  of  construction  and,  in  some  cases,  the  method  of  main- 
tenance which  are  adaptable  to  local  conditions  from  the  stand- 
points of  economy  and  efficiency. 


u 

*C  o 

.tj  > 

OJ 

| 

$& 

«  rt 

eal 
Pavement 

J 

rick  on 
Concrete 

one  Block 
on  Concre 

p 

jj 

ituminous 
Concrete 

ituminous 
Macadam 

ituminous 
on  Broken 

C  *J 
jj§ 

'gCO 

fi 

j 

CO 

M 

CO 

* 

u 

PQ 

M 

M 

M 

cq 

O 

W 

First  cost 

IO 

•I 

K 

T 

i 

6 

7 

7 

8 

9 

0 

Q 

TO 

Ease  of  traction  .  .  . 

IO 

TO 

8 

7 

9 

9 

9 

8 

8 

6 

6 

5 

2 

Non-slipperiness  

10 

4 

8 

7 

4 

6 

7 

7 

7 

8 

10 

10 

10 

Ease  of  cleaning  

IO 

IO 

9 

7 

9 

8 

9 

9 

9 

3 

3 

i 

I 

Noiselessness  

IO 

7 

6 

9 

6 

o 

o 

0 

TO 

TO 

TO 

TO 

Non-productive  of  dust.  .  . 

IO 

IO 

9 

8 

7 

7 

9 

8 

8 

6 

4 

3 

I 

As  an  aid  in  comparison  it  is  advisable  to  have  at  hand  a 
table  covering  numerical  values  of  certain  factors  which  are 
susceptible  to  such  form  of  comparison.  The  above  table, 
which  illustrates  the  treatment  of  the  problem  along  these  lines 


COMPARISON  OF   ROADS   AND   PAVEMENTS  399 

of  investigation,  gives  assigned  values  for  some  of  these  char- 
acteristics of  the  different  types  of  roads  and  pavements  on 
the  basis  of  ten  for  the  value  of  the  characteristic  in  an  ideal 
pavement. 

It  is  necessary  for  each  engineer  to  modify  tabular  informa- 
tion of  this  character  in  order  that  the  values  shall  be  based  upon 
local  conditions.  For  instance,  it  is  obvious  that  the  numerical 
values  assigned  to  "First  Cost"  will  vary  materially  in  different 
sections.  It  is  likewise  apparent  that  it  is  impracticable  to 
blindly  add  up  numerical  values  with  the  expectation  that  the 
type  having  the  highest  value  is  the  pavement  to  be  employed. 
In  the  great  majority  of  cases  one  or  more  factors  will  also 
have  a  greater  weight  than  certain  other  properties.  Of  course 
it  is  possible  to  weight  the  values  of  a  table  and  then  obtain 
totals  for  comparison.  The  totals  obtained  by  the  summation 
of  numerical  values  of  properties  referred  to  in  the  above  table 
must,  however,  be  supplemented  by  values  attributed  to  factors 
which  are  not  covered  in  the  table,  due  to  their  complex  and 
variable  character.  As  examples  of  such  factors  may  be  cited 
cost  of  maintenance,  durability,,  etc.,  which  properties  are  inti- 
mately related  to  local  conditions  pertaining  to  a  given  highway. 

Some  engineers  develop  a  classification  for  local  conditions 
based  on  the  foregoing  principles  and  as  each  individual  problem 
arises  assign  the  highway  in  question  to  a  given  class. 

John  A.  Brodie,  M.  Inst.  C.  E.,  while  Borough  Engineer  and 
Surveyor  of  Blackpool,  England,  divided  the  streets  within  his 
district  into  five  classes,  and  determined  the  amount  of  traffic 
for  which  each  class  was  suitable.  His  conclusions  were*  as 
follows : 

"Class  No.  i.  Foundation  of  Portland  cement-concrete  7 
inches  thick,  covered  with  granite  setts  5  inches  to  6  inches  in 
length,  3  inches  in  width,  and  6  inches  in  depth;  jointed  with 
fine,  dry  gravel  and  boiling  pitch  and  creosote  oil. 

"This  class  is  suitable  for  main  suburban  roads  with  traffic 
up  to  200,000  tons  per  yard  width  of  carriageway  per  annum; 
impervious  to  moisture;  noisy,  but  clean;  gradients  up  to 
i  in  40. 


400  ELEMENTS   OF   HIGHWAY   ENGINEERING 

"  Class  No.  2.  Foundations  of  Portland  cement-concrete  6 
inches  in  depth,  covered  by  specially  selected  Karri  or  Jarrah 
blocks  6  inches  to  8  inches  in  length,  3  inches  in  width,  4^ 
inches  in  depth,  laid  close,  direct  on  concrete,  and  grouted  with 
boiling  pitch  and  creosote  oil. 

"  Suitable  for  first-class  shop  streets,  with  traffic  of  about 
100,000  tons  per  yard  width  per  annum;  practically  impervious, 
noiseless,  clean,  and  dustless;  gradients  up  to  i  in  40. 

"Class  No.  3.  Foundations  of  hand-packed  rubble  8  inches 
in  depth,  covered  with  5  inches  of  tar-macadam. 

"  Suitable  for  residential  streets  having  a  light  traffic  of  20,000 
tons  per  yard  width  per  annum;  impervious,  noiseless,  clean, 
and  dustless;  gradients  up  to  i  in  24. 

"Class  No.  4.  Foundation  similar  to  No.  3,  but  7  inches 
deep,  with  2^-inch  gauge  water-bound  granite,  to  a  finished 
depth  of  5  inches,  blinded  with  fine  granite  chippings. 

"Suitable  for  ordinary  residential  front  streets  with  a  light 
traffic  of  about  5,000  tons  per  yard  width  per  annum;  pervious, 
comparatively  noiseless,  dusty,  and  sloppy;  gradients  up  to 
i  in  12. 

"  Class  No.  5.  Foundations  similar  to  Nos.  3  and  4,  7  inches 
in  depth,  covered  with  Haslingden  setts,  6  inches  to  8  inches 
in  length,  4  inches  to  6  inches  in  width,  and  6  inches  in  depth; 
jointed  with  dry  gravel  and  boiling  pitch  and  creosote  oil;  laid 
with  a  concave  cross-section  and  channel  in  center. 

"  Suitable  for  back  (or  secondary  access)  streets  9  feet  to  18 
feet  in  width,  with  a  traffic  of  60,000  tons  per  yard  width  per 
annum;  impervious,  clean,  and  dustless;  very  noisy;  gradients 
up  to  i  in  12. 

"It  is  not  claimed  that  the  above  classified  carriageway  speci- 
fications are  the  best  under  all  circumstances,  but  only  that 
they  are  probably  the  most  suitable  for  the  author's  district, 
or  for  use  under  similar  conditions." 

RECORDS  AND  COST  DATA.  It  is  apparent  that  records  and 
cost  data  are  essential  if  an  intelligent  comparison  is  to  be  made 
of  the  relative  value  of  different  types  of  roads  and  pavements. 


COMPARISON   OF   ROADS   AND   PAVEMENTS  401 

*"  Cost  records  of  highway  work  should  indicate  ,as  clearly  as 
possible  the  proportion  of  the  expense  chargeable  to : 

1.  Permanent  betterments,  such  as  land  purchases,  grading, 
the  improvement  of  lines  and  grades,  masonry  and  steel  bridges 
and  culverts.     This  part  of  the  work  once  done  may  be  con- 
sidered permanent  or  sufficiently  durable  to  outlast  more  than 
a  single  generation. 

2.  Curbing,  gutter  pavement,  fencing,  guard  rails,  wooden 
bridges,  concrete  foundation,  planting,  etc.,  all  of  which  may 
need  periodical  repairs,  but  will  probably  last  twenty  years  at 
least. 

3.  The  roadway  surface,  which  will  begin  to  deteriorate  at 
once,  and  will  need  constant  attention  and  periodical  renewal. 

"For  each  piece  of  work  the  records  should  include: 

1.  The  character  and  first  cost  of  the  materials. 

2.  Cost  of  delivery  on  the  work,  with  kind  of  transporta- 
tion and  distance  hauled. 

3.  Cost  of  labor  of  all  classes  and  the  quality  of  same. 

4.  Cost  of  present  value    of   plant    and    equipment,    with 
allowance  for  depreciation  due  to  the  work  under  construction 
and  not  previously  marked  off. 

5.  All  overhead  charges,  including  engineering  and  inspection. 

6.  Cost  of  bonds,  permits,  etc. 

7.  All  delays  due   to  weather,  failure  to  receive  materials, 
strikes,  or  other  causes. 

8.  A  precise  description  of  the  methods  employed  and  of 
the  surface  treatment  of  the  road. 

9.  A  statement  as  to  the  results    obtained,    the   probable 
causes  of  failures  or  unsatisfactory  work,  and  the  means  em- 
ployed to  correct  or  remedy  them. 

10.  The  manner  in  which  the  funds  to  pay  for   the  work 
are  raised,  whether   by  cash    appropriations,  by  the  issue  of 
bonds,  with  length  of  term  and  rate  of  interest,  or  by  money 
advanced  in  anticipation  of  the  collection  of   assessments  for 
benefit." 

*  Nelson  P.  Lewis,  Chief  Engineer  of  the  Board  of  Estimate  and  Appor- 
tionment, New  York  City,  1914  Transactions  Am.  Soc.  C.  E. 


402 


ELEMENTS   OF  HIGHWAY   ENGINEERING 


In  order  to  give  some  idea  of  the  detailed  information  rela- 
tive to  each  section  of  highway  which  should  be  recorded,  the 
1914  construction  and  the  1909  maintenance  report  forms  used 
by  the  Special  Committee  of  the  American  Society  of  Civil 
Engineers  on  "Materials  for  Road  Construction"  are  cited  as 
illustrations  of  forms  in  current  use. 

BITUMINOUS    MATERIALS    FOR    ROAD    CONSTRUCTION 
AND  STANDARDS  FOR  THEIR  TEST  AND  USE. 


SPECIAL  COMMITTEE  OF  THE 
AMERICAN  SOCIETY  OF  CIVIL  ENGINEERS 

Please  address  reply  to  Committee: 

A.  H.  BLANCHARD,  VV.  W.  CROSBY, 

Secretary  of  Committee,  Chairman; 

Columbia  University,  H.  K.  BISHOP, 

New  York  City.  A.  H.  BLANCHARD, 

A.  W.  DEAN, 
N.  P.  LEWIS, 
C.  J.  TILDEN, 
G.  W.  TILLSON. 


DATA  CONCERNING  THE  USE  OF  BITUMINOUS  MATERIALS  IN  SURFACES  AND 

PAVEMENTS. 


of 


GENERAL  INFORMATION. 

State County 

Town  or  City Highway 

Contractor 

Length  of  Work Width  of  Metal  (Average) .... 

Date  of  Beginning Date  of  Completion (of 

Bituminous  Materials) 

Method  of  Construction  (state  character  of  foundation,  thickness  of  courses, 

kinds  and  quantities  of  road  metal  and  of  bituminous  materials  used,  methods 

used,  and  approximate  maximum  grades). 

(Attach  copy  of  specifications  if  available.) 

AVERAGE  DAILY  TRAFFIC  AS  DETERMINED  BY  CENSUS 


One-horse  vehicles 

COMMERCIAL 

Passenger 
or 
Pleasure 

Empty 





Loaded 

I 

44       runabouts 

"       touring  cars  (open  or  closed) 

COMPARISON   OF   ROADS  AND   PAVEMENTS  403 

Are  widths  of  tires  on  horse-drawn  vehicles  regulated  by  law  or  ordinance? 

If  so,  please  state  regulations  on  separate  sheet. 

If  no  traffic  census  is  available,  give  estimate  of  traffic. 


Total  cost  of  bituminous  surface  or  pavement,  $ 

Cost  per  square  yard,  $ Average  thickness,  in  inches 

Average  wages  per  day,  of  common  labor,  $ .  .  .  .  Working  day  of hours. 

Description  of  Bituminous  Material  used. 

(State  type,  trade  name,  company  purchased  from,  and  if  supplied  by  con- 
tractor or  otherwise.) 
(If  analysis  is  available,  please  attach  copy  of  same.) 

REMARKS:  (Including  notes  as  to.  speed,  tire  widths,  and  any  preponderance 
of  traffic  at  certain  hours.) 


Name 

Title 

Address.  . 


Date 191 Reporting  Officer. 

AMERICAN  SOCIETY  OF  CIVIL  ENGINEERS. 


SPECIAL  COMMITTEE  ON 
BITUMINOUS  MATERIALS  FOR  ROAD  CONSTRUCTION. 

Please  address  reply  to  Committee: 

A.  H.  BLANCHARD,  W.  W.  CROSBY, 

Secretary,  Chairman; 

Columbia  University,  H.  K.  BISHOP, 

New  York  City.  A.  W.  DEAN, 

A.  H.  BLANCHARD, 

Secretary. 


To 


The  Committee  again  acknowledges  its  indebtedness  for  co-operation  in 
reporting  on  the  construction  of  roads,  in  connection  with  which  bituminous 
materials  were  used.  The  information  furnished  is  of  great  value,  but  in 
order  to  make  it  more  fully  available  it  seems  advisable  to  request  the  sup- 
plementary information  on  the  points  by  the  following  form. 

The  general  information  previously  furnished  has  been  filled  in  by  the 
Secretary. 

It  is  the  intention  of  the  Committee  to  ask  annually  for  reports,  each  to 
cover  a  year  of  observation,  and  it  is  hoped  that  this  form  will  be  returned 
as  soon  as  data  covering  a  year  are  available. 


404 


ELEMENTS   OF  HIGHWAY   ENGINEERING 


Report  on  Results  of  the  Use  of 
BITUMINOUS  MATERIALS  IN  ROAD  CONSTRUCTION. 


GENERAL  INFORMATION.     . 
(Required  for  identification  with  previous  reports.) 

State County 

Town Road 

Contractor 

Kind  of  bituminous  material 

Trade  name 

Method 

Dates  between  which  work  was  done to 

PERIOD  COVERED  BY  THIS  REPORT 

From to 

CLASS  OF  HIGHWAY  OR  NATURE  OF  TRAFFIC. 


AMOUNT  OF  TRAFFIC  OR  TRAFFIC  CENSUS  FOR HOURS  (Average)* 

Dates  of  census .  . 


Horse-Drawn    Vehicle 
Traffic. 
One-horse  veh  cles. 

Empty 
Vehicles 

Loaded 
Vehicles 

Est.  (in  Lbs.) 
of  Maximum 
Load  per 
Inch  of  Tire 

Passenger 
Vehicles 

Nov.  to 
March 

Apr.  to 
Oct. 

Nov.  to 
March 

Apr.  to 
Oct. 

Nov.  to 
March 

Apr.  to 
Oct. 

Nov.  to 
March 

Apr.  to 
Oct. 

Two     " 

Three  " 

Four    ' 

Five    "           ' 
Six    or    more    horse 
vehicles 

Motor-Vehicle    Traffic 
Motor  cycles 

runabouts 

"       touring      cars 
(four  or  five 
seats).      .    . 

touring    cars 
(six  or  seven 
seats)       in- 
cluding    li- 
mousines or 
landaulets 

"      wagons     or 
drays 

, 

*  If  possible,  "average  "  should  be  arrived  at  from  two  or  three  separate  determinations. 
State  number  of  determinations  from  which  average  is  secured. 


COMPARISON   OF    ROADS   AND   PAVEMENTS  405 

(1)  Date  of  opening  road  to  traffic,  or  average  length  of  time  after  com- 
pletion before  sections  of  road  were  opened  to  traffic. 

(2)  Has  the  surface  begun  to  disintegrate?     If  so,  when  and  in  what 
manner?     What  was  the  probable  cause? 

(3)  Has  any  displacement  of  the  surface  been  manifest  in  the  shape  of  ruts, 
waves,  etc.? 

(4)  Was  the  surface  objectionably  soft  in  hot  weather?     If  so,  state  air 
temperature;  also  state  maximum  temperature  at  which  surface  was  satis- 
factory. 

(5)  Is  the  tractive  effort  increased  by  the  presence  of  the  bituminous 
material? 

(6)  Was  the  surface  slippery  for  horses  or  motor  cars  in  (i)  cold  weather; 
(2)  when  wet;  (3)  on  frosty  mornings? 

(7)  Are  the  stones  of  the  top  course  of  the  macadam  visible?     If  so,  to 
what  extent? 

(8)  Has  the  surface  worn  differently  adjacent  to  curbs  and  car  rails  than 
it  has  in  the  traveled  ways? 

(9)  During  what  period  covered  by  this  report  was  the  surface  coated 
with  snow  or  ice? 

(10)   Maximum  depth  of  frost  in  this  period. 

(u)  Amount  of  rainfall  for  the  period  covered  by  this  report. 

(12)  Has  the  surface  been  artificially  watered?     If  so,  to  what  extent? 

(13)  Has  surface  been  cleaned?     If  so,  to  what  extent? 

(14)  Is  road  shaded  or  exposed? 

(15)  Cost  and  character  of  maintenance  during  period  covered  by  this 
report. 

(16)  Your  general  opinion  on  the  results  secured  on  the  above  road  and 
any  information  not  covered  properly  by  the  above  is  desired. 

(PLEASE  WRITE  ANSWERS  TO  FOREGOING  QUESTIONS,  REFERRING  TO  EACH 

BY  NUMBER.) 


Name 

Title 

Address . 


Reporting  Officer. 
Date 191.  ... 


CHAPTER  XX 
SIDEWALKS,  CURBS,  AND  GUTTERS 

The  design  and  construction  of  sidewalks,  curbs,  and  gutters 
constitute  an  important  part  of  the  work  of  a  highway  engineer. 

SIDEWALKS 

ESSENTIAL  QUALITIES.  There  are  several  essential  qualities 
which  a  sidewalk  should  possess.  The  surface  should  be  smooth, 
non-slippery,  non-porous,  agreeable  in  color,  low  in  first  cost 
.and  annual  cost,  easy  to  clean,  and  constructed  of  a  mate- 
rial which  will  wear  well.  When  used  on  a  business  street  the 
material  should  be  sufficiently  strong  to  resist  the  shocks  from 
falling  bodies  and  of  such  a  character  that  repairs  can  be  easily 
made. 

WIDTH  OF  SIDEWALK.  Sidewalks  in  business  districts  usually 
extend  from  property  lines  to  curbs.  In  residential  districts 
this  same  arrangement  may  be  used  or  a  space  for  a  grass  plot 
or  row  of  trees  may  be  left  between  the  edge  of  the  sidewalk 
and  the  curb.  In  some  cases  on  roads,  the  walk  is  entirely 
omitted  or  restricted  to  a  narrow,  footworn  path  on  the  side  of 
the  highway.  The  widths  of  sidewalks  from  property  line  to 
curb  vary  from  6  to  20  feet,  the  usual  width  for  each  sidewalk 
being  from  one-fifth  to  one-sixth  of  the  distance  between  property 
lines.  For  a  further  discussion  of  the  relation  of  the  width  of 
sidewalk  to  width  of  street  see  Chapter  IV. 

SLOPE  OF  SIDEWALKS.  It  is  essential  that  sidewalks  be 
pitched  so  as  to  shed  the  water  which  falls  upon  them.  This  is 
generally  accomplished  by  sloping  the  walk  from  the  property 
line  to  the  curb  by  an  amount  varying  from  y%  to  JA  inch  per 
foot,  depending  upon  the  kind  of  material  with  which  the  surface 
of  the  walk  is  constructed.  In  some  cases  the  high  point  of 

406 


SIDEWALKS,    CURBS,   AND   GUTTERS  407 

the  walk  is  made  near  the  center  and  the  surface  is  pitched  both 
ways.  This  arrangement,  however,  has  the  disadvantage  of 
throwing  part  of  the  water  towards  the  property,  of  being  ob- 
jectionable in  appearance,  and  uncomfortable  to  walk  upon. 

MATERIALS,  CONSTRUCTION,  COST  DATA.  The  materials  used 
in  the  construction  of  sidewalk  surfaces  are  artificial  flags,  asphalt 
mastic,  brick,  cinders,  cement-concrete,  gravel,  small  stone  setts, 
stone  flagging,  tar-concrete,  tile,  and  various  artificial  prepa- 
rations. 

Asphalt  Mastic.  This  type  of  pavement  is  constructed  in 
France  by  preparing  a  mastic  from  a  combination  of  rock  asphalt 
and  a  refined  asphalt  fluxed  with  an  asphaltic  base  petroleum. 
Sufficient  fluxed  asphalt  is  mixed  with  the  powdered  rock  asphalt 
so  that  the  mixture  will  contain  20  percent  of  bitumen.  A  layer 
of  this  mixture,  of  about  one  inch  in  thickness,  is  placed  on  a 
cement-concrete  foundation,  which  consists  of  about  four  inches 
of  concrete  and  a  layer  of  cement  mortar  from  ^  to  i  inch  in 
thickness.  A  scattering  of  gravel  is  spread  on  the  surface  and 
lightly  rolled  into  the  asphalt  mastic  while  the  latter  is  still  warm. 

Cost.  The  average  cost  of  this  pavement  in  France  is  ap- 
proximately $i  per  square  yard.  The  cost  of  a  similar  pavement 
in  England  is  about  $1.40  per  square  yard. 

Characteristics.  Footways  constructed  with  an  asphalt  mastic 
have  many  points  of  excellence.  They  are  practically  non- 
absorbent,  very  smooth,  without  joints,  pleasant  to  walk  upon, 
and  easily  maintained  and  repaired.  A  thickness  of  mastic  of 
^  of  an  inch  will  last  from  five  to  ten  years  and  sometimes 
longer  on  streets  where  the  traffic  is  not  heavy. 

Brick  and  Tile.  The  bricks  or  tiles  used  in  sidewalk  con- 
struction are  usually  made  of  burned  clay,  although  tile  made 
of  compressed  asphalt  is  used  to  some  extent.  Frequently  the 
surfaces  of  the  brick  or  clay  tile  are  stamped  in  the  process  of 
repressing  with  some  figure  of  fancy  design  in  order  to  add  to 
the  appearance  of  the  finished  walk.  In  France  the  usual  size 
of  tiles  used  is  5  to  5^  inches  square  and  i%  to  i>£  inches 
thick.  In  the  Netherlands  the  brick  are  7  inches  long  by  3^ 
inches  wide  by  2  inches  deep.  In  the  United  States  bricks  of 


408 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


the  ordinary  building  size  are  frequently  used.  Brick  sidewalks 
should  be  given  the  same  care  in  construction  as  is  accorded  a 
brick  pavement.  The  best  results  will  be  obtained  if  the  bricks 
are  laid  on  a  thin  sand  cushion,  about  ij/£  inches  in  depth, 
which  is  spread  over  an  accurately  surfaced  concrete  foundation, 
4  inches  thick,  and  the  joints  are  filled  with  a  bituminous  filler. 
The  bricks  are  usually  laid  flat  rather  than  on  edge,  and  with 
their  longest  dimensions  either  at  right  angles  or  diagonally  to 
the  curb  line.  Another  popular  arrangement  is  to  lay  the  bricks 
by  the  so-called  herring-bone  method.  Frequently  brick  side- 


inch  to  the  foot 


FIG.  173.     Cross- section  of  Brick  Sidewalk 
as  Constructed  in  Pittsburg,  Pa. 


walks  are  laid  on  a  bed  of  sand  placed  in  an  earth  trench  and 
the  joints  filled  with  sand.  It  is  not  surprising  to  find  that  a 
brick  sidewalk  constructed  in  this  manner  soon  loses  its  shape, 
due  to  the  displacement  of  the  bricks.  If  a  concrete  foundation 
is  not  used  a  foundation  of  good  gravel  or  cinders  should  be 
employed  underneath  the  sand  cushion.  This  type  is  shown  in 
Fig.  173,  which  is  the  standard  brick  sidewalk  as  constructed 
in  Pittsburg,  Pa. 

Cost.  The  cost  of  tile  paving  in  England,  the  tiles  being 
10  inches  by  5  inches  by  2>^  inches,  is  $1.62  per  square  yard. 
The  cost  of  constructing  tile  pavements  in  France,  the  tiles 
being  bedded  in  mortar  and  the  joints  filled  with  mortar,  varies 
from  $1.30  to  $1.50  per  square  yard.  The  cost  cf  brick  sidewalks 
in  Holland,  the  bricks  being  laid  in  a  sand  bed  on  a  concrete 
foundation  about  4  inches  thick  and  the  joints  filled  with  a 
cement  grout,  is  about  87  cents  per  square  yard.  In  the  United 
States  the  cost  of  brick  sidewalks  on  a  4-inch  concrete  foun- 
dation with  a  bituminous  filler  is  about  $1.75  per  square  yard. 


SIDEWALKS,    CURBS,   AND   GUTTERS  409 

Characteristics.  When  properly  constructed,  brick  sidewalks 
are  very  satisfactory.  They  are  non-slippery,  wear  well,  are 
easy  to  repair,  are  comfortable  to  walk  upon  when  smooth,  and 
are  easily  cleaned. 

Cinders.  Cinder  sidewalks  are  built  in  Chicago  by  depositing 
the  cinders  in  three  layers,  the  first  layer  being  9  inches  deep 
and  composed  of  coarse  material,  the  second  layer  3  inches  deep 
and  composed  of  fine  cinders,  and  the  third  layer  consisting 
of  fine  cinders  in  sufficient  amount  to  form  a  crown  to  the 
surface.  Each  layer  is  thoroughly  tamped  or  rolled.  Cinder 
sidewalks  may  be  built  very  cheaply  and  make  a  satisfactory 
surface  in  outlying  districts.  It  is  also  possible  to  use  the 
cinder  sidewalk  as  a  foundation  for  some  other  type  of  surface 
at  a  later  date. 

Cement-Concrete.  Cement-concrete  sidewalks  have  become 
very  popular  in  the  United  States  since  1910.  In  business 
districts  where  vaults  are  constructed  beneath  the  sidewalks, 
the  surface  is  frequently  composed  of  reinforced  concrete  slabs 
in  which  are  placed  plate  glass  shapes  for  the  purpose  of  light- 
ing the  vault. 

The  Concrete.  The  concrete  is  a  mixture  of  Portland  cement, 
sand,  and  broken  stone,  gravel,  or  slag. 

Subgrade.  Concrete  sidewalks  should  be  provided  with  a 
well  drained  foundation.  The  depth  of  excavation  to  the  sub- 
grade  will  depend  upon  the  climatic  conditions  and  the  nature 
of  the  ground.  In  places  where  frosts  occur,  it  may  be  necessary 
to  excavate  the  ground  for  a  depth  of  1 2  inches  or  more,  whereas 
in  places  where  there  is  no  frost,  4  to  6  inches  will  be  sufficient. 
Care  should  be  taken  in  completing  the  subgrade  that  the  material 
is  thoroughly  compacted  and  that  all  soft  and  defective  places 
are  removed  and  filled  with  good  material.  On  the  completed 
subgrade  is  built  a  subbase,  the  thickness  of  which  may  be 
12  inches  or  more  in  cold  climates  and  2  or  3  inches  in  some 
cases  where  the  soil  conditions  are  particularly  favorable.  A 
material  which  is  largely  used  for  a  subbase  is  cinders.  Broken 
stone,  sand,  gravel,  slag,  and  other  materials  are  also  used. 
Many  times,  in  reconstructing  old  tar-concrete  sidewalks,  the  old 


410 


ELEMENTS   OF   HIGHWAY   ENGINEERING 


surface  is  broken  up  and  put  into  the  subbase.  The  subbase 
should  be  thoroughly  compacted.  In  using  such  materials  as 
cinders  or  sand,  they  should  be  wet  down  during  the  process 
of  ramming  or  rolling.  In  some  cases  it  may  be  advisable  to 
drain  the  subbase.  This  is  accomplished  by  either  laying  tile 
drains  or  blind  stone  drains. 

Placing  the  Concrete.     The  concrete  is  usually  deposited  in 
two  layers,  a  base  layer  and  a  wearing  course.    The  thickness  of 


Rise-#  inch  to  the  foot 


l"of  Wearing  surface 


FIG.  174.     Cross-section  of  Cement-Concrete 
Sidewalk  as  Constructed  in  Pittsburg,  Pa. 


the  two  courses  will  depend  upon  the  traffic  conditions,  the 
climatic  conditions,  and  whether  or  not  the  sidewalk  is  situated 
in  a  place  where  heavy  goods  are  handled  on  it.  The  minimum 
total  thickness  of  concrete  is  usually  about  3^  inches,  made  up 
of  a  base  course  3  inches  thick  and  a  wearing  course  %  inch 
thick.  In  cases  where  the  traffic  conditions  are  severe  or  there 
is  much  frost,  the  total  thickness  may  be  made  as  much  as 
6  inches,  the  wearing  surface  being  from  i  to  2  inches  thick. 
The  standard  construction  in  residential  districts  of  Pittsburg, 
Pa.,  is  shown  in  Fig.  174. 

The  general  principles  relative  to  mixing,  handling,  and 
placing  concrete,  which  have  been  previously  mentioned  in 
Chapters  V  and  XIV,  apply  as  well  to  concrete  used  in  side- 
walk construction.  There  are  a  few  points,  however,  which  are 
peculiar  to  sidewalk  work.  The  concrete  should  never  be  laid 
as  a  monolithic  mass  unless  reinforced  with  steel,  but  should 
be  divided  into  separate  sections  by  joints  extending  through 
the  full  depth  of  the  concrete.  The  correct  size  of  slabs  has 
been  found  to  be  one  which  does  not  contain  over  36  square 
feet  of  surface  and  is  not  over  6  feet  in  any  one  direction.  The 
sections  are  obtained  by  constructing  either  wooden  or  steel 


SIDEWALKS,    CURBS,   AND    GUTTERS 


411 


forms  on  the  subgrade  corresponding  in  shape  an$  size  to  the 
section  desired.    The  forms  must  be  well  braced  and  of  sufficient 


FIG.  175.'     Straight- Edge  Used  in  Construction  of  Cement-Concrete 

Sidewalks. 


FIG.  176.     Use  of  Float  in  the  Construction  of  the  Surface  of  Cement-Concrete 

Sidewalks. 

rigidity  so  as  to  resist  springing  out  of  shape  as  the  concrete  is 
placed  in  them.     The  cross-forms  or  those  which  come  on  the 


412 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


lines  of  the  joints  between  adjacent  slabs,  are  preferably  made 
of  ^4-inch  metal  and  of  a  depth  corresponding  to  the  full  thick- 
ness of  the  proposed  walk.  When  metal  cross-forms  are  used,  the 
slabs  may  be  built  up  to  a  form  on  each  side,  and  when  the  con- 
crete has  set  the  metal  strip  may  be  withdrawn.  When  wooden 
cross-forms  are  used,  every  other  slab  is  built,  and  after  com- 
pletion the  cross-forms  are  removed  and  the  other  sections  are 
constructed.  The  joints  are  formed  by  laying  pieces  of  tar 
paper  against  the  faces  of  the  first  set  of  slabs. 


FIG.  177.     Bulging  of  Cement-Concrete  Sidewalk,  due  to  Expansion. 

The  concrete  for  the  base  course  should  be  thoroughly  tamped 
in  the  forms  until  the  required  thickness  is  obtained.  Before 
the  concrete  in  the  base  course  sets  up  the  wearing  course  should 
be  spread  upon  it.  The  concrete  in  the  wearing  course  is  mixed 
wetter  than  that  in  the  base  course.  It  is  shaped  and  spread 
by  means  of  a  straight-edge,  the  ends  of  which  generally  rest 
on  the  forms.  (See  Fig.  175.)  The  surface  is  then  smoothed 
off  with  trowels  or  a  wooden  float.  (See  Fig.  176.)  To 
roughen  the  surface  a  little  sand  may  be  scattered  over  it  and 
worked  in  during  the  process  of  smoothing.  A  soft  brush  or 
some  form  of  grooving  tool  may  be  used  to  mark  the  surface. 


SIDEWALKS,    CURBS,   AND    GUTTERS 


413 


Traffic  should  be  barred  from  the  sidewalk  for  a  week,  dur- 
ing which  time  the  surface  should  be  frequently  moistened. 
The  surface  should  also  be  covered  with  a  tarpaulin  or  other- 
wise protected  for  two  days  after  completion. 

Cost.  The  cost  of  cement-concrete  sidewalks,  including  exca- 
vation and  a  cinder  or  gravel  foundation,  varies  from  about 
80  cents  to  $1.50  per  square  yard. 

Characteristics.  Concrete  possesses  several  advantages  as  a 
sidewalk  material.  In  the  first  place,  the  materials  with  which 


FIG.  178.     Longitudinal  Crack  in  Cement-Concrete  Sidewalk,  due  to  Frost 

Action. 


it  is  constructed  are  available  in  many  localities.  It  makes  a 
durable  surface  if  properly  constructed,  is  not  slippery  under 
normal  conditions,  is  easily  cleaned,  is  more  or  less  impervious 
to  water,  and  its  cost  is  not  excessive.  Concrete  also  possesses 
the  advantage  of  being  easily  molded  into  any  form  desired. 
Moreover,  it  is  possible  to  incorporate  coloring  matter  in  the 
concrete  so  as  to  obtain  a  variety  of  colors.  When  con- 
structed in  conjunction  with  a  curb  and  gutter  built  of  the 
same  material,  it  gives  the  street  a  finished  appearance  which 
is  difficult  to  obtain  with  other  materials. 


414  ELEMENTS    OF  HIGHWAY   ENGINEERING 

Concrete  pavements  fail  many  times  by  the  slabs  bulging 
upward,  caused  frequently  by  the  heaving  action  of  the  frost 
or  because  the  slabs  have  been  pushed  up  by  the  roots  of  trees, 
or  it  may  be  due  to  insufficient  allowance  for  expansion.  The 
photographs  shown  in  Figs.  177  and  178  illustrate  this  type  of 
failure.  The  slabs  may  be  cracked  through  in  this  condition 
or  the  bulging  may  occur  so  that  all  the  heaving  takes  place 
at  a  joint  between  two  adjacent  slabs  without  breaking  them. 
Unequal  settlement  will  also  cause  the  slabs  to  be  displaced. 

Gravel.  Gravel  walks  are  laid  3  to  4  inches  thick  on  a  good 
subsoil.  Where  the  soil  is  poor  it  is  excavated  and  the  space 
refilled  with  crushed  stone,  clinker,  or  screened  gravel  of  large 
size.  The  total  depth  may  be  as  much  as  8  inches,  the  wearing 
course  being  ^  to  ^  inch  of  fine  gravel  or  torpedo  sand. 

Small  Stone  Setts.  Small  stone  sett  sidewalks  are  constructed 
in  many  towns  of  Portugal.  The  stones  are  laid  in  arcs  of  cir- 
cles or  in  figures  of  fancy  design,  different  colored  stones  being 
used,  thus  giving  a  contrast  in  color  very  pleasing  to  the  eye. 
In  Germany,  Kleinpflaster  is  used  to  a  considerable  extent  for 
sidewalks. 

Stone  Flagging.  Sidewalks  in  business  districts  are  frequently 
constructed  of  stone  flagging.  Stone  flagging  also  is  used  as  a 
surfacing  for  sidewalks  in  residential  districts  in  different  parts 
of  the  United  States  where  it  is  available.  Granite  and  sand- 
stone are  the  common  materials  from  which  the  slabs  or  flag- 
ging are  made.  Granite  slabs  6  inches  thick  are  laid  in  Paris 
for  sidewalks  on  some  of  the  principal  streets  which  carry  a  heavy 
foot  traffic.  Flagging  of  Yorkshire  or  Caithness  stone  is  very 
popular  throughout  certain  parts  of  England.  Artificial  flagging 
made  of  concrete  under  pressure  has  also  been  used  to  a  slight 
extent.  Fig.  179  shows  a  cross-section  of  the  standard  method 
of  constructing  flagstone  walks  in  Pittsburg,  Pa.  In  England 
both  the  natural  and  artificial  flagging  is  bedded  on  a  layer  of 
lime  mortar  which  rests  on  a  2  to  3-inch  course  of  clinkers.  The 
joints  are  filled  with  a  cement  mortar.  The  granite  slabs  used 
in  Paris  are  bedded  generally  on  a  concrete  foundation. 

The  Stone.     The  1912  specifications  of  the  Borough  of  the 


SIDEWALKS,   CURBS,   AND   GUTTERS 


415 


Bronx,  New  York  City,  require  that  new  flagstones  shall  be  of 
a  good  quality  of  sandstone  (bluestone),  with  a  fairly  smooth 
surface,  and  shall  measure  not  less  than  4  feet  in  width,  con- 
tain not  less  than  10  square  feet,  except  where  necessary  to  fit 
around  basin  heads,  and  shall  be  uniformly  not  less  than  3 
inches  in  thickness.  The  Yorkshire  flagging  used  in  England  is 


Rise-J<  inch  to  the  foot 


^  ^     *t>».^il»-«ir*    ^*...,.,    1  *....;., 


Broken  Stone  Drain 
every  25  ft. 


FIG.  179.     Cross-section  of  Flagstone  Sidewalk 
as  Constructed  in  Pittsburg,  Pa. 


required  to  be  K-mcn  thick  for  every  square  foot  of  surface 
and  of  such  a  size  that  there  will  not  be  more  than  14  slabs 
to  make  100  square  feet.  Artificial  flagging  is  made  in  slabs 
from  2  to  4  feet  square. 

Cost.  In  New  York  City  the  cost  of  bluestone  sidewalk 
flags  from  the  Hudson  River,  laid  in  place,  varies  from  $1.66 
to  $2.20  per  square  yard.  The  cost  of  walks  built  with  the  same 
material  in  Boston  varies  from  approximately  $2.50  to  $3  per 
square  yard. 

Characteristics.  The  life  of  granite  slab  sidewalks,  if  con- 
structed on  a  proper  foundation,  is  indefinite.  The  surface  wears 
smooth  in  time,  but  it  may  be  easily  roughened  by  means  of  a 
tooth  axe.  There  are  many  instances  in  England  where  flag- 
stone sidewalks  have  lasted  from  twenty-five  to  thirty  years. 
The  sidewalks  constructed  with  bluestone  flagging  in  this  country 
are  generally  quite  satisfactory,  except  that  in  many  instances 
the  flags  are  displaced  by  frost  action  or  other  causes. 

Tar-Concrete.  Tar-concrete  sidewalks  are  constructed  in 
many  places  in  the  United  States  and  England. 

Laying  the  Concrete.  This  type  of  surface  is  usually  con- 
structed in  two  or  more  courses,  the  materials  in  the  different 


416  ELEMENTS   OF   HIGHWAY   ENGINEERING 

courses  varying  in  size.  In  Newton,  Mass.,  a  three-course 
method  is  used,  the  different  courses  being  described  as  founda- 
tion course,  binding  course,  and  wearing  course.  The  foundation 
course  is  composed  of  coarse  gravel  from  2  to  4  inches  in  greatest 
diameter,  thoroughly  coated  with  hot  tar.  The  binding  course 
is  composed  of  clean  screened  gravel  not  exceeding  i  inch  in 
greatest  diameter,  which  is  heated  and  mixed  with  a  hot  coal- 
tar  composition  in  an  amount  of  about  one  gallon  of  the  bitu- 
minous material  to  i  cubic  foot  of  gravel.  The  wearing  course 
is  composed  of  screened  sharp  sand,  which  is  heated  and  mixed 
with  a  coal-tar  composition,  the  mixture  consisting  of  not  more 
than  75  percent  of  sand  and  not  less  than  25  percent  of  the 
bituminous  material,  by  weight.  The  surface  is  laid  to  a  total 
depth  of  3  inches.  Each  course  as  it  is  laid  is  thoroughly  tamped 
and  rolled.  The  binding  course  fills  the  voids  in  the  foundation 
course  to  a  large  extent.  The  total  thickness  of  these  two 
courses,  after  compaction,  is  not  less  than  2^  inches.  The 
wearing  course,  which  is  ^  of  an  inch  thick,  is  laid  and  rolled 
in  a  similar  manner.  The  top  surface,  which  is  usually  sprin- 
kled with  a  fine  sand  or  a  Portland  cement,  is  well  rolled. 

Cost.  The  cost  of  tar-concrete  sidewalks  in  the  United  States 
is  approximately  $0.60  per  square  yard. 

Characteristics.  Tar-concrete  sidewalks  usually  are  not  slip- 
pery. If  the  bituminous  material  is  of  the  proper  consistency 
the  surface  is  rather  elastic  and  pleasant  to  walk  upon.  The 
use  of  a  bituminous  material  not  possessing  the  proper  char- 
acteristics may  result  in  cracks  being  formed  in  the  surface  in 
cold  weather,  with  consequent  disintegration  of  the  pavement, 
or  in  warm  weather  the  tar  compound  may  soften  to  such  an 
extent  that  the  surface  becomes  objectionable  to  walk  upon. 
The  surface  is  easily  cleaned  when  intact  and  is  also  one  which 
may  be  easily  repaired.  Its  low  cost  has  led  to  its  general  use 
in  many  places,  although  at  the  present  time  it  is  being  replaced 
to  a  considerable  extent  by  cement-concrete. 


SIDEWALKS,    CURBS,   AND    GUTTERS  417 

CURBS  t 

Curbs  are  constructed  of  granite,  limestone,  sandstone,  and 
cement-concrete. 

STONE  CURBS.  Stone  curbs  are  made  from  4  to  12  inches 
wide,  8  to  24  inches  deep,  and  from  3  to  8  feet  long.  The  top 
and  front  faces  are  dressed,  the  latter  being  given  a  slight  batter, 
for  a  depth  somewhat  greater  than  the  exposed  part,  to  keep  the 
wheels  away  from  the  top  edge.  The  ends  are  square  dressed 
and  the  curbs  in  first-class  work  are  so  laid  that  the  ends  are 
about  yi  inch  apart. 

Laying  the  Curb.  Curbstones,  although  commonly  laid  on  a 
well-compacted  sand  base,  should  be  laid  on  a  base  of  concrete, 
broken  stone,  or  gravel.  The  broken  stone  or  gravel  is  carried 
well  up  around  the  base  of  the  curb,  as  shown  in  Fig.  179.  The 
trench  should  be  made  wide  enough  to  permit  thorough  ram- 
ming. In  Baltimore,  a  bed  of  gravel,  4  inches  deep,  is  Jaid  on 
the  bottom  of  the  trench  and  well  compacted.  The  curb  is 
laid  on  this  bed  and  set  to  the  line  and  grade.  The  remainder 
of  the  trench  is  filled  with  layers  of  well  compacted  gravel. 

Cost.  The  cost  of  a  granite  curb,  including  the  cost  of 
setting,  is  about  $i  per  linear  foot. 

CEMENT-CONCRETE  CURBS.  The  curbs  are  generally  built  in 
situ,  although  it  is  possible  to  make  them  at  some  central  point. 

Construction.  The  curbs  are  made  approximately  6  inches 
thick,  1 8  to  24  inches  deep,  and  from  8  to  10  feet  in  length. 
The  proportions  of  v  the  different  materials  used  in  the  concrete 
are  the  same  as  those  described  for  concrete  sidewalks.  The 
corner  next  to  and  above  the  gutter  is  always  molded  to  a 
radius  approximating  i><  inches  in  length.  Sometimes  this 
corner  is  formed  by  a  metal  strip,  having  the  desired  radius  of 
the  corner,  which  is  built  into  the  curb  at  the  time  the  concrete 
is  being  laid.  This  strip  is  anchored  to  the  body  of  the  curb  at 
three  or  four  points  in  each  length  of  8  to  10  feet  by  special  forms 
of  steel  tie  bars  that  are  firmly  attached  to  the  metal  strips. 
The  protection  afforded  the  edge  of  the  curb  by  this  metal 
strip  is  of  a  decided  advantage.  The  concrete  curb  and  a  con- 


418 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


2"Rad. 


I 

FIG.    1 80.     Cement-Concrete 
Curb  and  Gutter. 


crete  gutter  are  sometimes  constructed  as  one  piece,  in  which 
case  the  depth  of  the  curb  is  somewhat  less  than  in  the  case 
described  above,  as  the  base  of  the  curb  is  flush  with  the  base  of 

the  gutter.  (See  Figs.  180  and  181.) 
A  concrete  curb  should  be  con- 
structed on  a  bed  of  well  compacted 
sand,  gravel,  or  cinders,  in  the  same 
manner  as  described  for  stone  curbs. 
The  joints  between  adjacent  curbs 
are  made  by  placing  metal  plates  in 
the  forms  at  the  end  of  each  curb 
length.  The  concrete  is  filled  in  to 
the  plates,  and  after  it  has  obtained 
its  initial  set  the  plates  are  withdrawn, 

thus  leaving  a  joint.  When  the  curbs  are  built  at  the  same 
time  as  the  sidewalk  surface,  an  expansion  joint  should  be  left 
between  the  sidewalk  and  the  curb. 

Cost.  The  cost  of  concrete  curbing  8  inches  wide  by  24 
inches  deep  varies  from  30  to  40  cents  per  linear  foot. 

GUTTERS 

As  a  general  rule  paved  gutters  are  not  constructed  along 
the  sides  of  roads  except  on  grades  where  there  is  danger  of 
\vash-outs.  Paved  gutters  are  usually  built  on  streets  which 
are  curbed  and  which  have  the  roadways  constructed  with 
some  kind  of  improved  surfacing. 

MATERIALS.  Gutters  are  constructed  of  brick,  stone  block, 
cobblestone,  and  cement-concrete.  Cobblestone  is  extensively 
used  in  constructing  gutters  on  roads.  Cobblestone,  cement- 
concrete,  and  brick  gutters  are  frequently  built  adjacent 
to  broken  stone  surfaces  on  streets.  Brick  gutters  are  also  very 
popular  in  some  cities  where  sheet  asphalt  and  bituminous 
concrete  pavements  are  built. 

CONSTRUCTION.  Although  stone  block,  cobblestone,  cement- 
concrete,  and  brick  gutters  are  sometimes  constructed  with  the 
same  transverse  slope  as  the  adjoining  surface  of  the  carriage- 
way, it  is  better  to  increase  their  water-carrying  capacity 


SIDEWALKS,    CURBS,   AND    GUTTERS 


419 


either  by  building  them  on  a  sharper  slope  or  by  build- 
ing the  gutter  with  a  concave  curve  section.  The  depth  of  the 
gutter  at  the  center  of  the  curve  varies  from  4  to  9  inches, 
depending  upon  the  width  and  grade  of  the  gutter.  The  gutters 
are  built  from  2  to  6  feet  in  width,  depending  upon  the  amount 


FIG.  181.     Metal  Form  Used  in  the  Construction  of  a  Cement-Concrete  Curb 

and  Gutter. 

of  water  to  be  carried,  3  or  4  feet  being  widths  used  under  ordi- 
nary conditions.  Cobblestone,  cement-concrete,  and  brick  gut- 
ters are  commonly  constructed  on  a  foundation  of  sand,  gravel, 
or  cinders,  the  joints  being  filled  with  sand  or  poured  with  a 
cement  grout.  On  streets  a  concrete  foundation  is  frequently 
built  under  a  brick  gutter.  Since  the  cost  data  of  gutters  are 
the  same  as  that  of  the  different  types  of  paving  of  which 
they  are  composed,  information  in  regard  to  cost  may  be 
found  in  the  chapters  describing  the  construction  of  the  vari- 
ous pavements. 

COST  DATA 

SIDEWALKS,  CURBS,  AND  GUTTERS.  In  the  following  table 
are  given,  for  several  localities  throughout  the  United  States, 
the  average  1914  prices  of  sidewalks,  curbs,  and  gutters  con- 
structed with  various  materials. 


420 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


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CHAPTER  XXI 
HIGHWAY  STRUCTURES 

BRIDGES  AND  CULVERTS 

DETERMINATION  OF  WATERWAY.  The  first  step  in  designing  a 
bridge  or  a  culvert  is  to  determine  the  size  of  opening  necessary 
to  take  the  water.  The  following  methods  are  used  in  determin- 
ing the  size  of  opening  of  the  amount  of  water  for  which  provision 
must  be  made : 

Empirical  formulas,  which  give  either  the  area  of  opening  or 
amount  of  water. 

Observation  of  high-water  marks. 

Measurement  of  the  flow. 

The  factors  which  affect  the  amount  of  water  that  will  come 
to  any  particular  point  are  as  follows:  the  size  of  the  drainage 
area;  its  topography;  the  soil  conditions  throughout  the  area, 
whether  sandy,  rocky,  grass  land,  or  covered  with  forests;  the 
amount  of  rainfall  and  its  intensity;  and  climatic  conditions. 

Size  of  Drainage  Area.  Since  the  size  of  the  drainage  area 
enters  into  practically  all  of  the  calculations  required,  its  deter- 
mination will  be  considered  before  discussing  the  various  methods 
of  finding  the  size  of  opening.  Every  drainage  area  is  separated 
from  an  adjacent  drainage  area  by  a  divide  or  a  line  of  high 
ground.  The  drainage  area  for  a  culvert  or  a  bridge  will,  there- 
fore, include  all  of  the  area  above  the  structure  bounded  by  the 
line  of  the  divide.  The  drainage  area  may  be  determined  by 
actual  measurement  in  the  field  or  from  a  map.  The  field  survey 
may  be  made  by  running  a  traverse  line  around  the  boundary 
with  a  transit  and  stadia,  or  a  pocket  compass  may  be  used 
to  obtain  the  direction  of  the  boundaries  while  the  distances 
may  be  paced.  If  government  topographical  maps,  made  by 
the  Geological  Survey,  or  other  contour  maps  are  available,  the 
drainage  area  can  be  marked  off  by  tracing  out  the  divides 
from  the  contours  and  the  area  be  determined  by  planimeter  or 

421 


422  ELEMENTS   OF  HIGHWAY   ENGINEERING 

by  scale.  Besides  the  actual  size  of  the  area  it  is  necessary  to 
know  the  steepness  of  the  slopes  and  the  nature  of  the  soil 
conditions,  because  these  factors  affect  the  run-off  to  a  great 
extent.  Such  information  can  generally  be  determined  only  by 
examination. 

Empirical  Formulas.  Empirical  formulas  are  many  in  number 
and  give  results  which  are  extremely  variable.  This  may  be 
accounted  for,  in  some  instances,  by  the  fact  that  many  formulas 
are  based  on  local  conditions.  Some  of  these  formulas  contain 
only  one  variable,  namely,  the  drainage  area.  It  cannot  be 
expected  that  results  by  such  formulas  will  agree  with  those 
obtained  by  formulas  which  have  coefficients  that  are  to  be 
applied  for  different  soil  conditions,  steepness  of  slope,  etc. 

Myers  Formula.  A  formula  which  is  used  to  a  great  extent 
by  railroad  engineers  in  the  eastern  part  of  the  United  States 
is  the  Myers  formula  or  A  =  C  VZ),  in  which  A  is  the  area  of 
waterway  in  square  feet;  D  is  the  drainage  area  in  acres;  C  is 
a  variable  coefficient,  being  i  for  comparatively  flat  ground,  1.6 
for  hilly  compact  ground,  and  4  for  mountainous,  rocky  country. 
The  Myers  formula  has  been  found  to  give  satisfactory  areas 
for  small  openings. 

Talbot  Formula.  Another  noted  formula,  derived  by  Professor 
A.  N.  Talbot,  M.  Am.  Soc.  C.  E.,  from  the  Burki-Ziegler  formula, 
is  A  =  C  JJD3,  in  which  the  letters  have  the  same  significance 
as  described  above.  The  following  is  quoted  from  remarks  by 
Professor  Talbot  relative  to  the  value  of  the  coefficient  C:  "I 
conclude  that  for  rolling  agricultural  country,  subject  to  floods 
at  time  of  melting  snow,  and  with  the  length  of  valley  three 
or  four  times  the  width,  one- third  is  the  proper  value  for  C. 
In  districts  not  affected  by  accumulated  snow  and  where  the 
length  of  the  valley  is  several  times  the  width,  one-fifth  or 
one-sixth  or  even  less  may  be  used.  For  steep  and  rocky  ground 
C  varies  from  two-thirds  to  unity."  This  formula  has  been 
very  generally  adopted  in  the  West  and  Southwest. 

Observation  of  High  Water  Marks.  High  water  marks  are  of 
the  greatest  assistance  in  determining  the  size  of  opening  re- 
quired, particularly  if  they  are  measured  at  a  point  where  the 


HIGHWAY   STRUCTURES  423 

stream  is  narrow  and  the  bed  conditions  are  the  same  as  at 
the  time  of  the  occurrence  of  the  high  water.  It  should  be  re- 
membered, however,  in  seeking  evidences  of  high  water  that  the 
investigation  should  cover  a  long  period.  It  has  been  found,  in 
studying  the  flow  of  streams,  that  a  continuous  record  of  five 
years  will  not  usually  include  all  of  the  varying  conditions  of 
stage  to  which  streams  are  subjected.  The  measurement  of 
the  waterways  of  existing  bridges  along  the  same  stream  is  an 
excellent  guide  if  they  have  been  built  for  some  time. 

Measurement  of  Flow.  The  amount  of  water  may  be  deter- 
mined from  stream  measurements.  What  has  been  said  above 
in  regard  to  long  term  records  applies  in  this  case  as  well.  A 
record  of  stream  discharge  measurements  for  a  year  is  prac- 
tically worthless,  when  considered  by  itself,  for  the  determination 
of  the  size  of  required  opening.  It  is  possible  to  approximate 
the  run-off  from  a  drainage  area,  even  though  the  stream  has 
not  been  measured,  by  comparing  it  with  one  of  similar  charac- 
teristics where  the  run-off  has  been  determined.  In  such  a  case 
the  same  percentage  of  run-off  would  be  applied  to  the  amount 
of  water  falling  on  the  area  in  question. 

CULVERTS.  Culverts  are  commonly  classified  as  pipe,  box, 
and  arch.  Pipe  culverts  are  constructed  of  vitrified  clay,  cast- 
iron,  corrugated  metal,  concrete,  brick,  and  timber;  box  culverts 
are  built  of  stone,  concrete,  and  wood;  arch  culverts  are  con- 
structed of  stone,  concrete,  reinforced  concrete,  and  brick. 
The  selection  of  the  type  of  culvert  and  the  material  to  be  used 
is  largely  a  question  of  economy,  particularly  in  the  case  of 
small  waterways.  The  availability  of  materials,  their  first  cost, 
freight  charges,  cost  of  hauling,  and  cost  of  construction  all  have 
to  be  considered.  There  may  be  cases  where  considerations  other 
than  cost  would  determine  the  selection  of  the  type,  such  as,  for 
example,  the  depth  of  fill  over  the  culvert.  Some  kinds  of  pipe 
are,  however,  not  manufactured  in  diameters  of  over  3  feet. 
When  large  areas  of  waterway  are  required,  it  will  be  necessary 
to  use  either  a  culvert  of  the  box  or  arch  type  or  two  or  more 
lines  of  pipe,  the  selection  being  based  on  the  relative  economy 
and  durability  of  each  method. 


424  ELEMENTS   OF  HIGHWAY   ENGINEERING 

Design.  Culverts  are  required  to  support  the  weight  of  the 
material  which  covers  them  and  the  superimposed  loads.  They 
may  also  be  subjected  to  severe  expansive  forces  caused  by 
water  freezing  within  them.  The  amount  of  load  carried  to  the 
culvert  is  indeterminate  on  account  of  the  unknown  action  of 
earth  pressure  and  of  the  distribution  of  superimposed  loads. 
The  load  reaching  the  culvert  will,  therefore,  have  to  be  assumed. 
In  using  standard  pipes  of  cast-iron,  corrugated  metal,  or  vitrified 
clay,  it  is  ordinarily  not  necessary  to  investigate  their  strength, 
since  they  have  been  used  under  sufficiently  varying  conditions 
to  demonstrate  that  they  will  resist  successfully  any  load  that 
they  are  likely  to  receive,  provided  the  pipes  are  properly  placed. 
The  design  of  reinforced  concrete  and  concrete  pipes,  box  and 
arch  culverts  should  be  carefully  prepared  so  that  they  will 
support  the  loads  which  they  must  carry.  In  order  to  save 
work  necessitated  by  the  design  for  the  many  varying  condi- 
tions which  are  encountered,  it  is  customary  to  prepare  standard 
plans  of  these  types  of  culverts  which  are  designed  to  meet  a 
series  of  average  conditions. 

Location.  The  proper  location  for  a  culvert  can  only  be 
determined  by  an  examination  of  conditions  in  the  field.  It  is 
true  that  some  idea  as  to  the  need  of  a  culvert  may  be  gained 
from  looking  over  the  profile  of  a  highway  on  the  drawing, 
since  culverts  are  usually  needed  at  all  low  points  of  the  grade. 
When  these  places  are  examined  in  the  field,  however,  it  may  be 
found  that  the  ground  slopes  away  from  the  road  on  both  sides 
and  hence,  in  some  cases,  no  culvert  will  be  needed  to  carry  the 
water  across  the  road.  Other  places,  which  are  not  apparent  on 
the  plans,  may  be  found  by  a  field  examination  where  water 
will  pond  and  cause  property  damages  unless  a  culvert  is  con- 
structed to  remove  it.  In  cuts  with  shallow  side  ditches,  in 
localities  where  the  highways  are  curbed,  and  in  any  place  where 
it  is  not  possible  to  obtain  sufficient  cover  over  the  culvert  and 
still  have  the  inlet  end  of  the  culvert  above  the  surface  of  the 
ground,  some  form  of  catch-basin  or  drop  inlet  will  have  to  be 
built.  Small  culverts  of  the  pipe  or  box  type  and  small  arch 
culverts  are  usually  constructed  at  right  angles  to  the  axis  of 


HIGHWAY   STRUCTURES 


425 


the  road.  If  the  culvert,  when  used  on  hills  to  carry  the  water 
from  one  side  of  the  road  to  the  other,  is  placed  at  an  angle 
across  the  road  it  affords  a  somewhat  easier  access  to  the  water. 
This  scheme  is  also  used  in  some  cases  to  obtain  sufficient  cover 
over  the  culvert,  or  to  bring  the  point  of  outlet  to  a  more  con- 
venient place. 

Construction.  Culverts  of  all  types  should  be  built  on  a  stable 
foundation.  It  is  very  important  to  examine  the  material  of 
which  the  foundation  is  composed,  since  excessive  settlement 
causes  stresses  in  the  structure  that  it  is  not  designed  to  take. 
Pipe  culverts  should  be  firmly  bedded  on  the  foundation.  If 
the  soil  furnishes  a  very  poor  support  the  pipes  should  be  bedded 
in  a  layer  of  concrete  or  broken  stone.  Backfilling  for  pipe 


FIG.  182.     Headwall  with  Wing  Walls. 

culverts  should  be  composed  of  a  selected  fine  material,  free 
from  large  stones.  Care  should  be  taken  to  place  the  filling 
around  and  under  the  pipe,  tamping  the  material  in  thin  layers. 
Puddling  may  be  necessary  in  some  cases.  A  head  wall  should 
generally  be  constructed  on  both  ends  of  a  pipe  culvert.  The 
use  of  headwalls  makes  it  possible  to  use  a  somewhat  shorter 
culvert  than  would  otherwise  be  necessary.  Headwalls  for  small 
culverts  are  Usually  built  parallel  to  the  center  line  of  the  road. 
Sometimes,  however,  it  may  be  found  advisable  or  more  eco- 
nomical in  the  case  of  culverts  of  large  size  to  construct  wing 
walls,  either  straight  or  flared,  as  shown  in  Fig.  182.  Concrete 
and  stone  masonry  are  used  in  building  headwalls.  Cheapness, 
durability,  and  the  fact  that  concrete  can  be  molded  into  any 
form  desired,  renders  it  a  very  satisfactory  material  for  this 


426  ELEMENTS   OF  HIGHWAY   ENGINEERING 

purpose.  The  bottom  of  the  .headwall  should  be  carried  18 
inches  or  more  below  the  bottom  of  the  pipe  to  prevent  washing 
it  out. 

Vitrified  Pipes.  Vitrified  pipes  used  for  culverts  should  be 
the  best  quality  salt-glazed  sewer  pipe  of  the  dtfuble  strength 
type,  with  socket  joints.  This  pipe  is  made  in  2-foot  lengths 
with  diameters  from  12  to  36  inches.  The  pipes  are  so  laid  in 
the  trench,  with  the  socket  end  towards  the  inlet,  that  at  least  15 
inches  of  material  will  be  over  the  top  of  the  pipe  at  its  highest 
point.  Under  conditions  ordinarily  encountered  in  highway  work 


Courtesy  of  the  Gallon  Iron  Works. 

FIG.  183.     Corrugated  Metal  Pipe. 

vitrified  pipe  makes  a  very  satisfactory  as  well  as  a  cheap  culvert. 

Cast  Iron  Pipes.  Cast  iron  water  pipe  with  bell  and  spigot 
joints  has  been  used  in  culvert  construction  for  a  long  time. 
Standard  cast  iron  water  pipe  is  manufactured  in  1 2-foot  lengths 
and  hence  is  not  so  easily  adaptable  for  use.  Until  within  a 
few  years  the  standard  water  pipe  was  the  only  type  of  cast  iron 
pipe  available.  At  the  present  time  special  culvert  pipe  can  be 
obtained  which  is  made  in  4-foot  lengths.  A  special  type,  similar 
in  cross-section  to  a  spherical  triangle,  has  also  been  developed 
in  which  the  three  sides  are  shipped  as  separate  pieces  in  3-  to 
4-foot  lengths  and  are  fitted  together  in  "the  culvert  trench. 
Cast  iron  is  very  strong  and  will  last  for  many  years.  This  kind 
of  pipe  can  be  placed  within  6  inches  of  the  roadway  surface 
without  danger  of  breaking.  The  principal  objection  to  standard 
cast  iron  water  pipe,  outside  of  its  cost,  is  its  weight,  which 
makes  it  expensive  to  handle. 

Corrugated  Metal  Pipes.  Corrugated  metal  pipe,  see  Fig.  183, 
is  made  in  any  length  desired,  ranging  by  multiples  of  2  feet 


HIGHWAY   STRUCTURES 


427 


up  to  36  feet.  Since  it  weighs  about  one- twentieth, as  much  as 
cast  iron  it  is  much  more  easily  transported.  Care  should  be 
taken  to  select  pipes  of  the  proper  kind  of  metal.  Wrought 
iron  is  superior  to  steel  as  far  as  its  non-corrosive  properties 
are  concerned,  and  hence  pipes  made  of  iron  generally  have  a 
longer  life. 

Concrete  Pipes.  When  cast  previous  to  laying,  the  pipes 
are  made  in  lengths  of  from  4  to  8  feet,  with  thicknesses  varying 
from  2  to  6  inches,  depending  upon  the  diameter.  The  joints 
are  made  tapering,  with  some  form  of  socket  or  are  simply 
square-faced.  The  last  type  has  worked  out  very  satisfactorily 
in  practice. 

Drop  Inlets.  Frequently  the  inlet  end  of  a  culvert  will  have 
to  be  placed  some  distance  below  the  bottom  of  the  ditches 


<-l'8*-» 

-CD 

t 

<—  2W-> 

^ 

0 
"^H 

Y 

<-l'QL'^ 

Culvert 

JOHOOCO 

FIG.  184. 


With  good  f  oundation 
bottom  may  be  omitted 

Stone  Box  Inlet.      Maine  Highway  Department. 


leading  to  it.  Where  this  distance  is  not  great,  it  is  possible 
to  construct  a  drop  inlet,  which  is  an  open  box  of  concrete  or 
stone  masonry,  as  shown  in  Fig.  184.  In  case  the  inlet  is  far 
enough  removed  from  the  travelled  way  so  as  not  to  be  danger- 
ous to  the  traffic,  no  grating  over  the  top  is  necessary. 

Catch-Basins.  In  places  where  the  wash  carried  along  by  the 
water  is  of  large  amount,  a  catch-basin  is  more  serviceable  than  a 
drop  inlet  as  there  is  not  so  much  danger  of  the  pipe  becoming 
choked.  (See  Fig.  185.)  The  size  of  the  catch-basin  will  depend 
on  just  how  much  material  is  liable  to  be  washed  into  it  and  how 


428 


ELEMENTS   OF  HIGHWAY   ENGINEERING 


often  it  is  to  be  cleaned  out.  The  inlet  should  offer  as  little 
obstruction  as  possible  to  the  water,  and  the  grating  should  be 
of  such  a  form  as  not  to  be  dangerous  to  traffic.  The  outlet 


FIG.  185.     Location  Where  Catch-Basin  and  Culvert  Should  Have  Been  Used 
to  Take  Storm  Water  Under  the  Highway. 

pipes  of  catch-basins  in  cities  frequently  connect  with  sewers 
carrying  house  sewage,  and  it  is  essential  in  such  cases  that  the 


FIG.  1 86.     Concrete  Catch-Basin.     New  York  State  Highway  Department. 

pipes  be  trapped  in  order  to  prevent  the  emanation  of  objection- 
able gases  from  the  sewers.  A  cement-concrete  catch-basin  used 
on  roads  is  shown  in  Fig.  186,  and  a  brick  catch-basin  designed 
for  use  in  a  municipality  is  shown  in  Fig.  187. 


HIGHWAY   STRUCTURES 


429 


Inlet  Castings.    There  are  many  different  types  of  castings 
used  as  catch-basin  covers  and  inlets.    If  a  casting  is  so  placed 


Distance  to  be  determined 
actual  measurement  of  head  | 
to  be  used 


_  .Depth  of  Foundation 
-ij  Required  in  Rock 


VERTICAL  SECTION 


|  TOP  VIEW  AND*  HORIZONTAL  SECTION 
FIG.  187.     Brick  Catch-Basin.     Borough  of  the  Bronx,  New  York. 

that  traffic  will  pass  over  it,  a  very  strong  type  will  be  required. 
Fig.  1 88  shows  an  inlet  which  is  used  to  a  considerable  extent 
on  park  highways  and  on  roads  where  there  are  no  curbs.  Fig. 


430  ELEMENTS   OF   HIGHWAY  ENGINEERING 

189  is  a  view  of  the  iron  castings  used  in  the  construction  of  catch- 
basins  in  the  Borough  of  the  Bronx,  New  York  City. 

Stone  Box.    Stone  box  culverts  are  made  up  of  two  side  walls 
which  are  bridged  over  by  capstones.     If  the  stream  running 


Radius  as  Specified. 


Courtesy  of  the  Barbour  Stockwett  Co. 


FIG.  188.     Inlet  Casting.  FIG.  189.     Inlet  Casting.     Borough  of  the 

Bronx,  New  York. 

through  the  culvert  has  enough  force  to  cause  scour,  the  bed 
should  be  paved  with  cobblestones  or  other  suitable  material. 
The  side  walls  should  be  carried  to  a  good  depth  below  the 
bottom  of  the  stream  bed,  1 8  to  30  inches  generally  being  suffi- 
cient. The  side  walls  are  usually  constructed  of  dry  rubble 
masonry,  and  of  varying  thicknesses,  depending  upon  the  height 
of  opening.  It  is  good  practice  not  to  make  the  thickness  of  the 
wall  at  the  top  less  than  2  feet  even  in  the  smallest  size  culverts. 
While  the  faces  of  the  walls  are  generally  straight,  the  backs  of 
the  walls  are  sometimes  built  with  a  batter.  The  wings  of  the 
culvert  are  formed  by  extending  the  side  walls  out  straight  and 
stepping  them  down.  When  the  capstone  is  made  of  stone  slabs, 
the  specifications  usually  require  that  its  thickness  shall  be  at 
least  12  inches  for  all  sizes  up  to  4  feet.  Such  stones,  however, 
are  sometimes  difficult  to  obtain  and  are  expensive  to  handle, 
particularly  for  large  culverts.  Reinforced  concrete  slabs  are 
used  in  place  of  the  capstones  for  a  cover  in  some  cases.  Fig. 
190  shows  a  3  by  3  stone  box  culvert  as  constructed  by  the 
Massachusetts  Highway  Commission. 

Reinforced  Concrete  Box.     Reinforced  concrete  box  culverts 


HIGHWAY    STRUCTURES 


431 


are  built  in  a  manner  similar  to  stone  box  culverts,  except  that 
concrete  and  steel  are  used  throughout  in  their  construction. 
The  side  walls  are  made  quite  thin  in  comparison  with  those 
of  stone  box  culverts,  ranging  from  4  to  8  inches  in  thickness, 


t 


11- 


SIDE  ELEVATION 
WING  WALL 


SECTION 

FIG.  190.     Stone  Box  Culvert.     Massachusetts  Highway  Commission 


II  ff  (J  \ 

%  bars  8  o.c.          |       r^< 

M  bars  24"o.c. 


-f^ 


JL 


HALF 
SECTION 


HALF   END 
ELEVATION 


bars 


%bar 


FlG.  191.     Reinforced  Concrete  Culvert.     Massachusetts  Highway 
Commission. 

depending  upon  the  height.  In  the  larger  size  culverts,  the 
side  walls  are  reinforced.  Where  there  is  no  danger  of  scour  in 
the  stream  bed,  the  walls  are  carried  2  feet  below  the  stream 
bed,  and  a  footing  is  constructed  under  each  wall  which  is  from 
9  to  12  inches  in  thickness  and  of  a  width  sufficient  to  properly 


432 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


support  the  wall.  In  places  where  scour  may  occur,  a  concrete 
bottom  is  built  in  the  culvert  throughout  its  entire  length.  (See 
Fig.  191.) 

Timber  Box.     Where  other  materials  are  available  there  is 
no  excuse  for  building  a  timber  box  culvert  of  the  kind  that  is 


TV 


END  ELEVATION 


SECTION 
THROUGH   CULVERT 


FIG.   192.     Concrete  Arch  Culvert.     Massachusetts  Highway  Commission. 

frequently  encountered,  consisting  of  two  plank  sides  support- 
ing a  plank  top.  Such  construction  is  not  economical,  as  the 
planks  soon  rot  out  and  the  culvert  becomes  a  source  of  danger 
to  traffic. 

Arch  Type.  A  typical  small  arch  culvert  is  shown  in  Fig. 
192.  No  reinforcement  is  used  in  this  design  and  the  straight 
headwalls  are  placed  parallel  with  the  center  line  of  the  road. 

BRIDGES.  The  types  of  bridges  built  on  highways  may  be 
classified  as  follows: 


Joist  and  plank  floor 
Wood  trusses 
Wood  viaducts 

I-beams 

Place  girder,  through  and  deck 

Pony  trusses 

Trusses,  through  and  deck 

Viaducts 

Cantilevers 

Suspension  types 

Arch  ribs 

Draw  bridges 

Beams 

Girders 

Arches 

Arches 


Timber  bridges 
Steel  bridges 

Concrete  and  Reinforced  Concrete 
Stone 


HIGHWAY   STRUCTURES  433 

The  selection  of  the  type  of  bridge  best  suited  for#ny  crossing 
is  governed  by  the  cost  of  the  structure,  its  appearance  and 
adaptability.  Conditions  at  some  crossings,  such  as  headroom, 
requisite  waterway,  character  of  foundations,  elimination  of  piers, 
or  the  maintenance  of  a  navigable  channel  preclude  the  use  of 
certain  types  which  otherwise  might  be  desirable.  Generally  too 
much  importance  is  attached  to  the  first  cost.  Many  of  the 
steel  bridges  in  country  towns  are  sold  to  the  town  representa- 
tives without  the  services  of  an  engineer.  The  decision  as  to 
the  type  of  structure,  whether  it  is  a  girder,  pony  truss,  or 
through  truss,  rests  largely  with  the  contracting  bridge  company, 
since  the  townspeople  are  dependent  upon  its  advice.  It  is  not 
surprising,  therefore,  that  many  of  the  existing  steel  bridges 
neither  look  well  nor  give  good  service.  Very  little  attention 
is  given  in  this  country  to  aesthetics  in  bridge  design,  par- 
ticularly in  steel  bridges  of  the  small  types.  The  use  of  rein- 
forced concrete  structures  of  both  the  arch  and  girder  type, 
however,  has  made  it  possible  to  erect  structures  which  harmonize 
with  the  environments. 

Design.  Bridges  should  not  be  designed  to  carry  less  than 
a  i5-ton  road  roller.  The  maximum  live  load  to  be  used  will 
depend  upon  local  conditions.  Care  must  be  taken  to  obtain 
a  firm  foundation  for  all  substructures  and  to  make  provision 
against  all  possibility  of  scour.  The  abutments  and  piers  may  be 
built  of  stone  masonry  or  concrete,  the  latter  material  being 
used  to  a  large  extent  for  this  purpose. 

Location.  The  problem  of  location  for  a  bridge  requires 
more  study  than  in  the  case  of  a  culvert.  The  location  will 
affect  the  selection  of  the  type  of  structure  to  some  extent.  In 
certain  cases  it  may  be  found  that  the  required  area  of  water- 
way will  necessitate  raising  the  grade  on  the  approaches.  If  the 
alignment  of  the  highway  on  either  side  of  the  stream  is  not  good 
it  may  be  advisable  to  shift  the  location  of  the  bridge  up  or  down 
stream  from  the  original  location,  with  a  consequent  improve- 
ment of  the  alignment.  There  may  be  occasions  where  lack  of 
good  foundations  procurable  at  a  reasonable  cost  would  warrant 
placing  the  bridge  at  a  point  where  good  foundations  will  be 


434  ELEMENTS    OF   HIGHWAY   ENGINEERING 

readily  accessible,  the  saving  in  cost  of  the  substructure  being 
more  than  enough  to  pay  for  the  relocation  of  the  approaches. 

Bridge  Floors.  The  floor  systems  on  which  the  wearing 
surfaces  rest  are  of  two  principal  types,  solid  floor  systems, 
generally  composed  of  concrete,  and  the  open  framework  system, 
formed  by  intersecting  stringers  and  floorbeams.  The  first  type 
is  common  to  all  concrete  structures.  It  is  possible,  when  this 
type  is  used,  to  build  on  it  any  type  of  roadway  that  may  be 
desired,  provided  the  structure  is  designed  to  take  the  load.  Both 
types  of  floor  systems  are  used  on  steel  bridges.  The  solid 
floors  are  made  up  of  concrete  arches  between  longitudinal  or 
transverse  steel  beams,  of  concrete  on  buckleplates  supported 
on  a  steel  framework,  of  concrete  on  a  floor  of  riveted  steel 
shapes,  of  reinforced  concrete  slabs  supported  on  a  steel  frame- 
work, or  of  reinforced  concrete  slabs  and  beams  in  cases  where 
the  steel  framework  is  omitted.  The  same  remarks  apply  rela- 
tive to  the  construction  of  the  wearing  course  on  these  types  of 
solid  floors  as  were  stated  above  relative  to  roadways  on  con- 
crete structures.  When  some  one  of  the  above  types  of  solid 
floors  is  not  used  in  connection  with  steel  bridges,  the  framework 
composed  of  the  steel  floorbeams  and  stringers  is  covered  with 
a  plank  floor,  which  may  act  as  the  wearing  course  itself  or  may 
support  a  wearing  course  of  some  other  kind  of  material.  With 
the  exception  of  bascule  bridges  the  type  or  form  of  steel  struc- 
ture has  no  bearing  on  the  type  of  floor  system  or  wearing  course 
to  be  used.  The  wearing  course  on  a  solid  floor  of  either  a 
concrete  or  steel  structure  may  consist  of  earth,  gravel,  or  broken 
stone,  or  cement-concrete,  bituminous,  brick,  stone  or  wood 
block  pavements.  When  the  steel  framework  of  the  floor  system 
is  covered  with  planks,  they  may  serve  as  the  wearing  course 
or  may  support  a  wearing  surface  of  any  one  of  the  following 
types:  another  layer  of  planks,  a  wood  block  pavement,  or  a 
brick  pavement.  When  a  two-layer  plank  floor  is  built  the 
planks  in  one  layer  are  placed  at  right  angles  to  the  center  line 
of  bridge  and  the  planks  in  the  other  layer  are  laid  on  lines  at 
45  degrees  with  the  center  line  or  vice  versa. 

Steel  Bridges.     The  life  of  a  steel  bridge,  if  properly  con- 


HIGHWAY    STRUCTURES  435 

structed  and  maintained,  is  generally  stated  to  be  frpm  forty  to 
fifty  years.  The  character  and  amount  of  the  traffic  usually 
changes  materially  during  this  time,  hence  a  new  structure  may 
be  required  in  a  comparatively  short  period,  although  the  bridge 
has  not  deteriorated  to  an  extent  which  would  require  renewal. 
Many  small  bridges  which  are  built  by  contract  on  the  lump 
sum  basis  are  so  skimped  in  material  that  their  life  may  not  be 
over  ten  years.  The  floor  systems  of  steel  highway  bridges 
generally  deteriorate  much  more  rapidly  than  the  main  members, 
due  to  the  fact  that  there  are  many  more  places  for  the  dirt  to 
lodge.  Water  wets  the  dirt  and  soon  rust  begins  to  form,  which 
rapidly  eats  away  the  steel.  A  steel  bridge  should  be  painted  at 
least  once  every  three  or  four  years  and  perhaps  more  often, 
depending  upon  climatic  and  other  conditions.  Steel  near  salt 
water,  where  the  spray  can  reach  it,  rusts  rapidly  and  re- 
quires frequent  painting.  The  floor  systems  of  bridges  over 
railroad  tracks  which  are  exposed  to  the  gases  from  the  smoke 
stacks  of  the  engines  will  require  painting  with  special  kinds  of 
paint  in  order  to  protect  the  metal.  Bridge  painting  is  un- 
fortunately entirely  neglected  in  many  small  towns,  with  the 
consequent  rapid  deterioration  of  the  bridges. 

I-Beam  Bridges.  I-beams  with  the  ends  resting  on  a  beam 
supported  by  vertical  supports  or  with  the  ends  resting  on  abut- 
ments of  either  stone  or  concrete  masonry  are  commonly  used 
for  short  spans.  The  former  is  called  a  leg  bridge  and  cannot 
be  recommended.  The  maximum  economical  span  is  about 
32  feet. 

Pony  Truss  and  Plate  Girder  Bridges.  When  the  span  is 
such  that  I-beams  are  no  longer  economical,  either  a  riveted 
pony  truss  or  a  plate  girder  may  be  used.  Low  truss  bridges  are 
economical  up  to  spans  of  about  80  feet,  while  the  limiting  span 
of  plate  girder  bridges  is  about  100  feet.  It  is  doubtful,  how- 
ever, whether  either  of  these  types  are  economical  when  com- 
pared with  a  concrete  structure.  The  construction  of  pony 
truss  bridges,  with  light  sections,  cannot  be  recommended.  If 
such  a  structure  is  to  be  used,  it  should  be  built  with  an  excess 
of  metal  over  and  above  what  is  required  in  order  to  provide 


436 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


requisite  stiffness  and  rigidity  to  the  structure.  Pin-connected 
pony  trusses  should  never  be  built. 

Pin-Connected  and  Riveted  Trusses.  Both  pin-connected 
and  riveted  trusses  with  parallel  chords  are  used  for  spans  from 
80  to  170  feet  in  length.  For  spans  over  170  feet,  trusses  with 
inclined  upper  chords  are  usually  employed. 

Timber  Bridges.  Timber  highway  bridges  are  not  generally 
constructed  at  the  present  time  except  as  temporary  structures. 
Considered  from  any  other  standpoint  the  construction  of  timber 
bridges  is  uneconomical  and  unwise,  due  to  their  rapid  deteriora- 
tion and  the  liability  of  their  being  destroyed  by  fire. 

Concrete  and  Reinforced  Concrete  Bridges.  Since  1905 
the  increase  in  the  use  of  concrete  for  structures  of  all  kinds 


\^-~  3  Diams.  C.  to  C. 

FlG.   193.     Reinforced  Concrete  Girder  Bridges.     Illinois  Highway 
Commission. 

has  been  very  rapid.  The  use  of  reinforced  concrete  has 
made  it  possible  to  construct  bridges  for  many  spans  for  which 
plain  concrete  bridges  could  not  be  economically  built.  If  the 
structure  lies  under  a  heavy  fill,  any  material  increase  in  the 
live  load  will  not  increase  the  stress  in  the  structure  to  any 
great  extent,  since  the  dead  load  is  large  in  proportion  to  the 
live  load.  The  ease  with  which  concrete  can  be  molded  into 
different  shapes  makes  it  possible  to  add  greatly  to  the  appear- 
ance of  the  structure  without  materially  increasing  the  cost. 

Girder  Bridges.  The  simplest  types  of  reinforced  concrete 
bridges  are  the  deck  girder  and  through  girder.  The  Illinois 
Highway  Commission  has  developed  a  reinforced  concrete  girder 


HIGHWAY   STRUCTURES  437 

bridge  of  the  through  type  which  has  been  used  to  a  considerable 
extent  throughout  that  State  for  spans  up  to  60  feet  in  length. 
Fig.  193  shows  a  cross-section  of  this  bridge  and  the  general 
scheme  of  reinforcement. 

Arch  Bridges.  Arch  rings  are  built  with  the  intrados  line 
conforming  to  either  a  semi-circular,  segmental,  parabolic,  ellip- 
tical, or  some  multiple  centered  curve.  The  semi-circular  arch 
has  been  used  to  a  great  extent.  Reinforced  concrete  arches  with 
flat  curves  have  frequently  been  constructed.  The  flatter  the 
arch  the  greater  the  thrust  on  the  abutment,  hence  care  should 
be  taken  to  see  that  the  foundation  provided  under  the  abut- 
ment is  capable  of  withstanding  this  pressure.  The  ratio  of 
the  span  to  rise  will  usually  be  determined  by  physical  condi- 
tions, such  as  the  waterway  required,  headroom,  grade  of  road- 
bed, location  of  piers,  cost  of  foundations,  and  appearances. 

GUARD  RAILS 

Guard  rails  should  be  placed  at  the  tops  of  all  embankments 
and  at  culvert  ends  where  there  is  the  slightest  element  of 
danger.  Wood,  iron,  and  concrete  are  the  materials  used  in 
the  construction  of  guard  rails.  Guard  rails  are  placed  12  inches 
from  the  edges  of  the  embankment  toward  the  center  of  the 
road;  on  concrete  or  masonry  headwalls  they  are  placed  generally 
in  the  center  of  the  masonry. 

On  concrete  bridges  of  the  deck  type,  side  rails  may  be 
made  of  pipe  railing  or  some  form  of  concrete  fencing.  Bridges 
of  the  through  girder  type  of  steel  or  concrete  do  not  need  any 
railing  unless  the  span  is  so  short  that  the  depth  of  the  girders 
is  not  high  enough  to  afford  sufficient  protection.  The  fencing 
on  steel-truss  bridges  is  made  of  pipe  or  railing  composed  of 
steel  shapes  riveted  together. 

WOOD  RAILS.  Wooden  guard  rails,  see  Fig.  194,  are  usually 
built  so  that  the  top  rail  is  about  3  feet  6  inches  above  the 
ground.  The  posts  are  spaced  8-feet  center  to  center.  The 
top  rail  is  set  cornerwise  in  V-shaped  notches  sawed  in  the  tops  of 
the  posts  or  the  tops  of  the  posts  are  sawed  off  slanting  towards  the 


438 


ELEMENTS   OF  HIGHWAY   ENGINEERING 


center  of  the  road  and  the  top  rails  nailed  to  the  inclined  faces. 
The  top  of  the  lower  rail  is  placed  about  i  foot  3  inches  below 
the  bottom  of  the  top  rail.  All  joints  and  exposed  surfaces  are 
well  painted  with  a  light-colored  paint,  white  lead  often  being 
specified  for  this  purpose.  The  first  cost  of  wooden  rails  in 


FIG.  194.     Wooden  Guard  Rail. 

place  is  ordinarily  between  20  and  30  cents  per  linear  foot 
and  the  cost  of  maintenance  is  from  5  to  6  cents  per  linear  foot 
per  year. 

Iron  rods  are  sometimes  used  in  place  of  wooden  posts  where 
a  guard  rail  is  needed  for  a  culvert  headwall  or  for  a  ledge. 
The  top  of  the  rod  is  forked  to  receive  a  square  wooden  rail. 
The  lower  rail  is  frequently  omitted. 

PIPE  RAILS.  Gas  pipe  railing  is  also  used  on  headwalls  of 
culverts,  or  on  ledges.  (See  Fig.  195.)  The  pipe  used  is  i>£  or 
2  inches  in  diameter.  The  railing  is  about  3  feet  6  inches  high 
and  is  built  with  two  or  three  lines  of  pipe.  The  iron  posts 
are  generally  spaced  8  feet  center  to  center.  The  pipes  are 
fixed  at  the  bottom  by  anchoring  the  bases  in  the  ledge  or  con- 
crete, or  else  the  bottoms  are  set  in  a  cast  iron  flange  which  is 
bolted  to  the  ledge  or  masonry.  The  cost  of  gas  pipe  railing  is 
about  75  cents  per  linear  foot. 


HIGHWAY    STRUCTURES 


439 


CONCRETE  RAILS.  Concrete  guard  rails  consist  of  concrete 
rails  set  on  top  of  concrete  posts.  (See  Fig  195.)  The  rails  are 
built  with  a  rectangular  trough  section  fitted  with  cross  dia- 
phragms connecting  the  sides  and  top.  The  rails  are  generally 
reinforced  and  are  set  about  3  feet  2  inches  above  the  ground. 


FIG.  195.     Gas  Pipe  Railing  and  Concrete  Guard  Rails. 

The  cost  of  concrete  guard  rails  is  estimated  to  be  about  50 
cents  per  linear  foot. 

PARAPET  WALLS.  On  masonry  bridges  and  retaining  walls, 
parapet  walls  that  serve  as  guard  rails  are  constructed  above 
the  level  of  the  roadway.  The  walls  are  a  part  of  the  rest  of 
the  structure  and  are  built  of  the  same  material.  This  type  of 
construction  generally  gives  the  structure  a  better  appearance 
than  any  of  the  types  of  guard  rails  heretofore  described.  It 
is  also  stronger  and  involves  no  maintenance  costs.  These  ad- 
vantages render  the  construction  of  parapet  walls  advisable  where 
masonry,  bridges  and  retaining  walls  are  constructed. 

HIGHWAY  SIGNS 

ROAD  SIGNS.  On  highways  outside  of  urban  districts  the 
signs  usually  employed  consist  of  (i)  direction  and  distance 
signs,  (2)  danger  signs,  and  (3)  highway  department  signs. 


440  ELEMENTS   OF  HIGHWAY  ENGINEERING 

Direction  and  Distance  Signs.  The  fundamental  principle 
of  the  design  of  direction  and  distance  signs  is  that  they  should 
be  so  constructed  and  so  located  on  the  highway  that  the  requi- 
site information  may  easily  be  read  by  drivers  of  vehicles  when 
at  a  reasonable  distance  from  the  signs.  It  is  necessary  in 
order  to  meet  the  above  requirement  to  reduce  the  information 
on  the  sign  to  a  minimum.  The  National  Tourist  Office  of 
France  has  accomplished  the  most  notable  work  in  this  field 
of  highway  engineering.  Among  the  important  conclusions 
reached  by  this  Office  are  (i)  that  it  is  sufficient  to  erect  plates 
at  those  crossings  or  intersections  where  confusion  might  arise; 
(2)  that  plates  should  be  placed  at  right  angles  to  the  direction 
of  the  road;  (3)  that  for  each  road  at  an  intersection  the  sign 
should  contain  the  names  and  distances  of  only  two  urban  dis- 
tricts and  that  one  name  should  be  that  of  the  next  urban 
district  on  the  given  road;  (4)  that  the  empirical  formula 

10,000 
L  =   -         -  p  indicates  the  distance  which  a  word  is  legible 

o 

to  a  person  with  average  eyesight  when  the  letters  are  p  thick, 
5/>  high  and  p  apart. 

Danger  Signs.  Four  danger  signs  have  been  adopted  by  the 
Department  of  Roads  and  Bridges  of  France.  These  signs, 
which  are  placed  on  the  highway  from  500  to  1,000  feet  from 
the  source  of  danger,  indicate  the  following  obstacles  and  dangers : 
(i)  turnings;  (2)  obstacles  along  the  road  such  as  ditches,  humps, 
bridges,  etc.;  (3)  barriers,  road  crossings  or  railroad  crossings 
when  protected  by  barriers,  except  where  such  crossings  should 
be  classed  as  dangerous  crossings;  (4)  dangerous  crossings,  road 
crossings  or  railroad  crossings  when  not  protected  by  barriers. 
One  or  more  of  these  signs,  which  include  a  sign  representative 
of  the  kind  of  danger  and  its  name,  have  been  adopted  in  many 
localities  of  Europe  and  in  a  few  sections  of  the  United  States. 

Highway  Department  Signs.  Highway  number  and  designa- 
tion signs,  milestones,  and  section  monuments  have  not  been 
standardized.  Many  countries  of  Europe  and  several  States  in 
America  have  adopted  standards  of  their  own.  Fig.  196  shows 


HIGHWAY   STRUCTURES  441 

the  type  of  sign  and  post  used  in  1914  by  the  New  York  State 
Highway  Department. 

STREET  SIGNS.     In  urban  districts  the  signs  which  are  in 
common  use  include  street  designation  signs,  general  direction 


FIG.  196.     Highway  Department  Sign  Post,  State  of  New  York. 

and  speed  signs  for  through  traffic,  and  a  large  variety  of  signs 
used  by  police  authorities  for  the  proper  regulation  of  traffic. 

CAR  TRACKS 

It  was  pointed  out  in  Chapter  IV,  from  the  standpoint  of 
the  efficient  design  of  the  highway,  the  location  of  car  tracks 
within  the  limits  of  the  roadway  is  accompanied  by  several 
disadvantages.  The  progress  and  social  development  of  com- 
munities, however,  are  dependent  to  a  large  extent  upon  trans- 
portation facilities.  Street  railways  and  motor-buses  are  the  two 
systems  which  must  be  considered  in  designing  the  highways. 
Although  it  is  reasonable  to  expect  that  motor-buses  may  re- 
place surface  railways  in  many  instances,  it  is  doubtful  if  their 
use  will  become  so  common  that  transportation  by  electric  trac- 
tion railways  on  roads  and  streets  will  be  entirely  eliminated. 
The  problem  is  to  construct  the  railways  so  that  all  of  the 


442  ELEMENTS   OF  HIGHWAY   ENGINEERING 

advantages  can  be  enjoyed  and  all  of  the  disadvantages  will 
be  reduced  to  a  minimum.  This  involves  a  consideration  of  the 
location  of  the  tracks  and  details  of  track  construction. 

LOCATION.  There  are  several  advantages  in  having  the  car 
tracks  located  on  a  part  of  the  highway  which  is  inaccessible  to 
other  traffic.  This  arrangement  does  not  interfere  with  the  con- 
venience of  those  entering  and  leaving  the  cars  and  has  the 
added  advantage  that  the  cars  can  be  operated  at  higher  speeds 
without  danger  to  other  traffic.  The  work  incident  to  the  main- 
tenance of  the  tracks  can  be  carried  on  without  disturbing  the 
surfacing  of  the  roadway,  and  obviously,  since  the  tracks  are 
without  the  roadway,  the  wear  of  the  latter  is  not  affected  by 
their  presence.  From  the  standpoint  of  the  traction  companies 
several  advantages  may  be  noted.  The  cost  of  the  original  con- 
struction is  generally  much  less  than  when  the  tracks  are  located 
within  the  roadway,  due  to  the  fact  that  the  special  methods  of 
construction  are  not  required.  The  expenses  of  maintenance  are 
less  than  where  the  tracks  are  so  situated  that  they  can  be  used 
by  all  kinds  of  traffic.  The  arrangement  above  described  may 
be  accomplished  in  cases  of  wide  residential  streets  or  boule- 
vards, where  the  tracks  may  be  located  either  at  the  sides  or 
in  the  center  of  the  highway.  There  are  very  few  instances  in 
cities  of  this  country,  however,  where  this  arrangement  is  em- 
ployed except  in  the  case  of  boulevards. 

The  usual  practice  is  to  have  the  car  tracks  located  within 
the  roadway,  either  in  the  center  or  at  the  sides,  the  tracks 
being  made  flush  with  the  adjoining  pavement  so  as  to  offer  as 
little  obstruction  as  possible  to  other  vehicular  traffic.  Whether 
the  tracks  should  be  located  in  the  center  or  at  the  sides  is 
dependent  upon  local  conditions,  but  primarily  depends  upon 
the  width  of  the  roadway.  In  Chapter  IV,  the  New  York  City 
ordinance  was  quoted  as  requiring  a  minimum  width  of  roadway 
of  30  feet  for  streets  in  which  there  is  a  single  track  railroad 
and  40  feet  for  those  in  which  there  is  a  double  track  railroad. 

The  following  physical  data  must  be  taken  into  consideration 
in  the  determination  of  location.  The  width,  out  to  out,  of  cars 
varies  from  8  to  9  feet.  The  clearance  allowed  between  passing 


HIGHWAY   STRUCTURES  443 

cars  on  a  double  track  is  variable,  depending  somewhat  upon 
the  speed.  It  is  generally  a  minimum  of  5  inches' and  may  be 
as  much  as  2  feet  on  very  wide  streets,  where  there  is  ample 
room.  The  usual  track  gauge  in  this  country  is  4  feet  8^ 
inches.  If  a  standard  gauge  is  used  and  a  minimum  clear- 
ance, the  distance  center  to  center  of  tracks  for  the  widest  cars 
will  be  9  feet  6  inches,  and  the  total  width,  out  to  out,  of  cars 
on  the  tracks  will  be  practically  14  feet. 

TRACK  CONSTRUCTION.  Experience  has  shown  that  the  main- 
tenance of  a  roadway  surface  adjacent  to  a  car  track  is  usually 
more  costly  than  other  portions  of  the  surface.  Water,  which 
seeps  down  by  the  rail,  particularly  at  the  joints,  softens  up 
the  underlying  soil  with  the  result  that  the  track  pumps  and 
the  adjacent  pavement  is  soon  disintegrated.  Sometimes  the 
surface  of  the  rail  head  as  it  comes  from  the  rolls  is  more  or 
less  uneven  and  wavy.  The  treads  of  car  wheels  may  wear  un- 
evenly, and  this,  together  with  the  unevenness  of  the  rails,  pro- 
duces vibrations  which  are  very  injurious  to  the  adjoining  pave- 
ments. Sheet  asphalt  and  other  types  of  bituminous  pavements 
are  particularly  susceptible  to  a  very  small  movement  of  the 
rail,  both  laterally  and  vertically. 

Rails.  Among  the  earliest  types  of  rails  was  a  flat  stepped 
head  which  was  spiked  to  a  wooden  stringer,  the  stringers  resting 
on  wooden  cross-ties.  The  traction  companies  in  those  times 
were  not  obliged  to  build  their  tracks  so  as  to  offer  minimum 
obstruction  to  other  traffic.  In  fact,  one  type  of  rail  developed 
in  New  York  City,  was  designed  with  the  intent  of  being  so 
objectionable  that  the  vehicles  would  keep  off  of  the  car  tracks. 
This,  like  the  first  rail  described,  was  a  rail  head  which  was 
spiked  to  a  wooden  stringer.  Instead  of  being  a  stepped  head, 
however,  with  one  side  flush  with  the  pavement,  the  rail  head 
projected  above  the  surface  of  the  surrounding  pavement  in  the 
form  of  an  inverted  U,  the  car  wheels  having  a  center  groove. 
The  railway  companies  soon  appreciated  that  more  permanent 
construction  was  necessary,  and  many  types  of  rails  were  devel- 
oped in  which  the  head  could  be  removed  when  worn  and 
replaced  with  a  new  piece,  the  web  and  rail  base  remaining 


444 


ELEMENTS   OF  HIGHWAY  ENGINEERING 


permanently  in  place.     Stepped  heads  and  those  with  a  groove 
similar  to  the  ones  in  use  to-day  were  also  tried. 

The  types  of  rails  now  used  are  the  grooved  rail,  the  stepped 
rail,  and  the  T-rail,  as  shown  in  Figs.  197,  198,  and  199,  respec- 

7 

T" 


JL 


FIG.  197.     Grooved  Rail. 


FIG.  198.     Stepped  Rail. 


tively.     When  the  car  track  occupies  a  space  inaccessible  to 
other  traffic  it  is  quite  customary  to  use  the  T-rail.    Although 

this  form  of  rail  is  also  adopted 
sometimes  for  track  construction 
within  the  roadway,  special  means 
are  taken  to  form  a  groove  so  that 
the  result,  as  far  as  the  traffic  is 
concerned,  is  practically  the  same 
as  if  a  grooved  rail  had  been  used. 
A  rail  with  a  stepped  head  has 
been  commonly  used,  but  offers 
considerably  more  obstruction  to 
traffic  than  a  grooved  rail.  The 
smoothest  track,  from  the  stand- 
point of  other  traffic  crossing  over 
it,  is  without  doubt  constructed  with  grooved  rails.  This  type  is 
now  being  largely  employed  both  in  this  country  and  in  Europe. 


FIG.  199.     T-Rail. 


HIGHWAY   STRUCTURES 


445 


Rails  are  made  of  different  depths,  varying  from  about  4  to  9 
inches.  The  Q-inch  rails  are  generally  designated  as  girder  rails. 
A  rail  of  this  depth  is  required,  if  a  form  of  pavement  such  as 
wood  block,  stone  block,  or  sheet  asphalt,  etc.,  is  to  be  built 
next  to  the  track,  in  order  to  give  sufficient  room  for  a  proper 
thickness  of  concrete  over  the  tie  to  support  the  pavement  above. 
Foundation.  The  simplest  form  of  track  foundation  is  that 
of  imbedding  wooden  ties  in  gravel  or  broken  stone.  This  method 
is  ordinarily  used  in  roadways  for  tracks  constructed  on  roads 


BLOCK  STONE  PAVING 


Sub-grade  for  gravel 
foundation 


Set  flush  with  top  of  Rail 


ASPHALT  PAVING 
FIG.  200.     Track  Construction,  City  of  Pittsburg. 

surfaced  with  broken  stone  or  similar  material,  and  for  tracks 
that  are  built  on  a  right  of  way  which  is  inaccessible  to  other 
traffic. 

It  is  essential  in  track  construction  which  is  flush  with  the 
loadway  and  adjacent  to  pavements  of  wood  block,  granite 
block,  brick,  or  any  form  of  bituminous  pavement  to  provide  a 
foundation  that  will  make  the  track  as  rigid  as  possible.  The 
work  should  be  done  in  such  a  manner  as  to  reduce  to  a  minimum 
the  maintenance  and  renewal  work.  To  provide  a  permanent 
foundation,  concrete  is  used.  The  ties  are  laid  on  a  bed  of 


446 


ELEMENTS    OF   HIGHWAY   ENGINEERING 


ballast  or  concrete  which  extends  underneath  the  full  width  of 
track.  Concrete  is  filled  around  and  in  some  cases  over  the 
ties.  Fig.  200  shows  the  foundation  required  for  tracks  laid 
adjacent  to  stone  block  and  sheet  asphalt  pavements  in  the 
City  of  Pittsburg,  Pa.  In  this  construction  a  stone  drain,  lead- 
ing from  the  foundation  underneath  the  track  to  the  gutter 
drain,  is  required  every  25  feet.  It  is  very  important  that  the 
track  should  be  thoroughly  drained,  as  otherwise  the  water 
which  seeps  through  will  soften  the  foundation.  In  some  cases 
the  wooden  cross-ties  are  omitted  and  a  longitudinal  support 
of  concrete  is  built  under  each  rail.  (See  Fig.  201.)  The 
rails  are  tied  together  at  intervals  with  tie  rods,  which  are 


Cement  Mortar 


T 

4 


From  Tillson's  "Street  Pavements  and  Paving  Materials." 

FIG.  201.     Longitudinal  Support  for  Rail. 

imbedded  in  the  concrete  between  the  rails.  Special  forms  of 
support  for  the  rails  have  to  be  used  in  some  cases  where  the 
third  rail  or  other  device  for  delivering  the  current  is  below  the 
ground.  In  Germany  molded  reinforced  concrete  blocks  have 
been  laid  underneath  the  rails.  The  blocks  are  5  inches  thick, 
31  inches  long,  and  20  inches  wide,  and  are  so  molded  that  in 
the  top  surface  a  trough  is  provided  which  is  wide  and  deep 
enough  so  that  when  the  rail  is  set  in  it  the  head  of  the  rail 
will  be  flush  with  the  surface  of  the  block. 

Surfacing  Adjacent  to  Rails.  The  franchises  of  street- 
railway  companies  generally  stipulate,  both  in  this  country  and 
in  Europe,  that  the  company  shall  construct  and  maintain  the 


HIGHWAY   STRUCTURES  447 

pavement  over  the  area  covered  by  its  tracks  and  for  a  distance 
from  1 8  inches  to  2  feet  outside  of  the  rail  adjacent  to  the  road- 
way. The  franchises  also  usually  require  the  traction  com- 
panies, to  maintain  the  pavement  next  to  the  rails  in  as  good 
condition  as  the  adjoining  pavement.  The  enforcement  of  these 
stipulations  has  been  extremely  difficult  in  certain  localities. 


FIG.  202.     Asphalt   Blocks  Adjacent  to  Outside   Rails  and  Stone     Blocks 

Between  Rails. 

It  has  been  found  necessary  to  use  special  methods  of  con- 
struction along  and  between  the  rails  in  order  to  procure  the 
best  results. 

If  the  rails  are  of  sufficient  depth  to  provide  room  for  the 
block  and  a  firm  foundation  over  the  ties,  brick,  wood  and  stone 
block  pavements  can  be  constructed  up  to  and  between  the 
rails.  Although  bituminous  pavements  are  constructed  up  to 
and  between  the  rails,  better  results  have  been  obtained  when 
some  form  of  blocks  has  been  placed  between  the  edge  of  the 
pavement  and  the  rail,  as  shown  in  Fig.  202.  There  are  in- 
stances where  a  track  is  paved  with  granite  or  brick  blocks  for 
the  full  width  between  the  rails  and  for  18  inches  to  2  feet 
outside  regardless  of  the  type  of  surfacing  in  the  remainder 
of  the  pavement.  The  space  on  either  side  of  the  rail  web 


148  ELEMENTS   OF  HIGHWAY  ENGINEERING 

underneath  the  rail  head  is  generally  filled  with  cement  mortar, 
as  is  shown  in  Figs.  200  and  201.  Some  engineers  believe  that 
the  best  results  are  obtained  by  using  a  low  penetration 
bituminous  material  which  is  not  objectionably  susceptible  to 
changes  in  temperature. 

On  roads  where  tracks  are  constructed  with  shallow  rails 
resting  on  ties  imbedded  in  gravel,  bituminous  concrete  and 
bituminous  macadam  constructed  adjacent  to  the  rail  will  not 
wear  satisfactorily.  In  cases  where  the  rails  are  so  shallow 
that  blocks  cannot  be  laid  on  edge  between  them  and  the  pave- 
ment as  previously  described,  an  1 8-inch  strip  of  water-bound 
gravel  or  broken  stone  has  been  found  to  work  satisfactorily. 
Paving  blocks  laid  flat  and  cobblestones  have  also  been  used 
with  good  results. 

PIPE  SYSTEMS 

KINDS  OF  SYSTEMS.  Pipe  systems  are  to  be  found  beneath 
streets  in  all  cities.  The  business  of  some  corporations  con- 
trolling subsurface  systems  is  so  far-reaching  in  extent  that  their 
service  pipes  extend  into  the  outlying  districts  beyond  the  city 
proper.  As  a  general  r.ule  water  supply  pipes  and  pipes  for 
the  conveyance  of  sewage  are  the  first  systems  installed  in  the 
development  of  a  city.  The  universal  use  of  gas  as  a  means  of 
light  adds  one  more  pipe  service  which  must  be  so  placed 
as  to  be  available  to  the  abutting  property.  Telegraph, 
telephone,  and  electric  light  wires,  were  formerly  carried 
above  the  ground.  Although  this  practice  is  still  com- 
mon, in  the  business  districts  of  many  large  cities  the  wires 
are  now  being  laid  in  conduits  below  the  surface.  Vaults  under- 
neath the  sidewalks,  subways  underneath  the  streets,  car  tracks 
on  the  surface  with  their  special  construction  sometimes  for 
carrying  current  beneath  the  surface,  pipes  for  carrying  heat  or 
refrigerating  fluids  from  a  central  plant,  pneumatic  tubes,  pipes 
for  house  connections,  are  all  present  in  many  cases  to  further 
complicate  the  problem.  An  engineer  must  assume,  then,  that 
pipes  for  sewage,  water,  and  gas  are  an  essential  part  of  the 
development  of  any  built-up  district,  and  in  designing  the  streets 


HIGHWAY   STRUCTURES  449 

due  allowance  must  be  made  for  the  accommodation  of  such 

0  • 

systems. 

These  systems  are  not  all  built  at  the  same  time.  The  water 
supply  and  sewage  systems  are  generally  installed  by  the  mu- 
nicipality, the  custom  being  to  build  and  extend  these  systems  as 
the  growth  of  the  locality  demands.  The  gas  pipes,  conduits 
for  telephone,  telegraph,  or  electric  light  wires  may  be  laid  by 
many  different  corporations  and  at  various  times.  In  a  great 
many  of  our  cities  extremely  poor  records,  showing  the  location 
of  their  services,  have  been  kept  by  these  private  corporations. 
With  all  of  these  various  systems  underneath  the  surface  of 
the  street  it  is  not  surprising  that  the  streets  are  continually 
torn  up.  This  condition  of  affairs  can  only  be  alleviated  by 
proper  administration  and  legislation. 

Pipe  Subways.  The  use  of  subways,  in  which  all  pipe  systems 
might  be  placed,  would  do  away  with  a  great  deal  of  the  trouble 
of  street  disturbances  which  are  now  so  prevalent  in  those  places 
where  pipe  systems  exist.  The  construction  of  subways  for  this 
purpose,  however,  is  very  costly  and  for  this  reason  would  be 
financially  impracticable  except  in  the  busiest  .and  most  im- 
portant streets  of  large  cities.  Many  European  cities  have  pipe 
subways  of  varying  lengths.  In  London  there  is  a  total  of  about 
seven  miles.  In  Paris  .the  sewers,  which  are  of  large  dimension, 
are  used  for  pipe  subways.  It  is  the  belief  of  many  engineers 
that  the  gas  pipes  should  be  excluded  from  subways  in  which 
electric  cables  are  placed,  because  of  the  danger  of  explosion. 
The  experience  of  Paris  has  been  that  this  danger  is  largely 
eliminated  if  the  subway  is  well  ventilated. 

Location.  Many  of  the  services  enumerated  above  have 
connections  running  to  the  houses  which  face  on  the  street,  and 
therefore  they  must  be  placed  somewhere  between  the  property 
lines.  This  available  space  is  generally  divided  into  two  side- 
walks and  one  or  more  roadways.  In  some  cases  a  narrow 
parking  space  is  left  between  the  curb  of  the  walk  and  the  paved 
sidewalk,  which  plan,  however,  will  generally  only  be  found  in 
the  residential  parts  of  a  city.  Unless  the  sidewalks  or  parking 
spaces  are  very  wide  it  is  necessary  to  locate  some  of  the  pipe 


450  ELEMENTS   OF  HIGHWAY  ENGINEERING 

systems  in  the  roadway.  Where  vaults,  which  extend  to  the 
surface,  are  constructed  underneath  the  sidewalk,  the  use  of 
the  space  underneath  the  sidewalk  is  no  longer  available  for 
the  services.  As  was  mentioned  in  Chapter  IV,  ordinances  in 
some  cities  now  prevent  the  construction  of  such  vaults  within 
a  distance  nearer  than  four  feet  to  the  surface  of  the  sidewalk, 
thus  leaving  this  space  for  the  location  of  subsurface  pipes. 

It  is  rarely  feasible  to  have  a  roadway  of  a  street  without  any 
pipe  systems  beneath  it.  The  principle  to  be  kept  in  mind  is 
to  place  those  systems  beneath  the  roadway  which  will  be  dis- 
turbed the  least.  They  should  be  located  in  such  a  manner  that, 
if  repair  work  is  necessary,  it  may  be  accomplished  with  a  mini- 
mum disturbance  of  traffic.  If  all  of  the  different  systems  can 
be  laid  in  a  street  before  the  roadway  is  surfaced,  and  if  the 
house  connections  can  be  extended  to  the  property  lines  at  the 
same  time  the  installation  of  the  different  systems  is  made,  such 
a  procedure  will  prevent,  to  a  large  extent,  disturbances  to  the 
roadway  at  later  periods. 

REPAYING  TRENCHES.  It  is  very  difficult  to  properly  repave 
a  surface  over  a  trench  which  has  been  made  for  the  purpose  of 
installing  or  repairing  pipe  systems.  There  is  more  or  less 
settlement  of  the  earth  in  the  trench,  which  will  cause  a  similar 
depression  in  the  surface.  The  fact  that  the  pavement  replace- 
ments are  not  properly  supervised  and  that  frequently  the  work 
is  done  by  people  not  familiar  with  the  details  of  construction, 
gives  results  which  are  particularly  unsatisfactory.  It  is  essential 
that  the  earth  in  being  rilled  back  in  the  trench  should  be  thor- 
oughly compacted.  This  can  be  accomplished  by  tamping  the 
earth  in  very  thin  layers.  Puddling  the  earth  with  water  will 
also  aid  compaction.  When  the  pavement  in  which  the  trench 
has  been  cut  is  supported  upon  cement-concrete,  the  foundation 
may  be  replaced  by  either  of  the  following  methods  in  order 
to  give  it  additional  strength:  first,  the  depth  of  the  concrete 
may  be  increased;  second,  it  may  be  reinforced  and  tied  into 
the  adjoining  concrete;  third,  it  may  be  cut  away  on  strips 
adjacent  to  the  trench  and  rebuilt  by  bridging  the  trench. 


APPENDIX  I 

GLOSSARY  OF  TERMS  APPLICABLE  TO  HIGHWAY 
ENGINEERING 

In  the  glossary  will  be  found  some  terms  and  definitions 
adopted  by  the  Special  Committee  on  "Materials  for  Road 
Construction"  of  the  American  Society  of  Civil  Engineers  noted 
thus  f,  others  adopted  by  the  American  Society  for  Testing 
Materials  designated  thus  *,  and  others  proposed  by  the  Com* 
mittee  on  "Standard  Tests  for  Road  Materials"  (Committee 
D-4)  of  the  American  Society  for  Testing  Materials,  which 
have  been  indicated  thus  {. 

Aggregate.  The  mineral  material,  such  as  filler,  sand,  gravel, 
shells,  slag,  or  broken  stone,  or  combinations  thereof,  with  which 
the  cement  or  bituminous  material  is  mixed  to  form  a  mortar 
or  concrete.  Fine  aggregate  may  be  considered  as  the  mineral 
material  which  will  pass  a  ^-inch  screen  and  coarse  aggregate 
the  material  which  will  not  pass  a  j^-inch  screen. 

Amorphous.  A  textural  term  used  to  describe  a  rock  struc- 
ture without  definite  form  or  crystalline  composition. 

Aqueous  Rocks.  Rocks  which  have  been  formed  through  the 
agency  of  water. 

Arkose.    A  coarse  feldspathic  sandstone. 

Asphalt.ft  Solid  or  semi-solid  native  bitumens,  solid  or 
semi-solid  bitumens  obtained  by  refining  petroleums,  or  solid 
or  semi-solid  bitumens  which  are  combinations  of  the  bitumens 
mentioned  with  petroleums  or  derivatives  thereof,  which  melt 
on  the  application  of  heat,  and  which  consist  of  a  mixture  of 
hydrocarbons  and  their  derivatives  of  complex  structure,  largely 
cyclic  and  bridge  compounds. 

Asphalt  Block  Pavement,  f  One  having  a  wearing  course  of 
previously  prepared  blocks  of  asphaltic  concrete. 

fDec.,  1914  Proceedings,  Am.  Soc.  C.  E.t  1915  Report  of  Special  Com- 
mittee on  "Materials  for  Road  Construction,"  pages  3011-3019. 

451 


452  ELEMENTS  OF  HIGHWAY  ENGINEERING 

Asphalt  Cement,  f  A  fluxed  or  unfluxed  asphaltic  material, 
especially  prepared  as  to  quality  and  consistency,  suitable  for 
direct  use  in  the  manufacture  of  asphaltic  pavements,  and  having 
a  penetration  of  between  5  and  250. 

Asphaltenes.f  J  The  components  of  the  bitumen  in  petroleum, 
petroleum  products,  malthas,  asphalt  cements,  and  solid  native 
bitumens,  which  are  soluble  in  carbon  disulphide,  but  insoluble 
in  paraffin  naphthas. 

Asphaltic.  f    Similar  to,  or  essentially  composed  of,  asphalt. 

Bank  Gravel.  {  Gravel  found  in  natural  deposits,  usually 
more  or  less  intermixed  with  sand,  clay,  etc.;  gravelly  clay, 
gravelly  sand,  clayey  gravel,  and  sandy  gravel  indicate  the 
various  proportions  of  the  admixture  of  the  finer  materials. 

Basalt.  A  general  name  given  to  dark,  basic,  volcanic  rocks 
of  wide  distribution,  and  in  a  restricted  sense  employed  as  a 
rock  name  for  porphyritic  and  felsitic  rocks  consisting  of  augite, 
olivine,  and  plagioclase  with  varying  amounts  of  a  glassy  base 
which  may  entirely  disappear. 

Base.f    Artificial  foundation. 

Binder,  f  (i)  A  foreign  or  fine  material  introduced  into  the 
mineral  portion  of  the  wearing  surface  for  the  purpose  of  assist- 
ing the  road  metal  to  retain  its  integrity  under  stress,  as  well 
as,  perhaps,  to  aid  in  its  first  construction.  (2)  The  course,  in  a 
sheet  asphalt  pavement,  frequently  used  between  the  concrete 
foundation  and  the  sheet  asphalt  mixture  of  graded  sand  and 
asphalt  cement. 

Bitumen,  f*  A  mixture  of  native  or  pyrogenous  hydrocarbons 
and  their  non-metallic  derivatives,  which  may  be  gases,  liquids, 
viscous  liquids,  or  solids,  and  which  are  soluble  in  carbon  di- 
sulphide. 

Bituminous  Cement.  |  A  bituminous  material  suitable  for 
use  as  a  binder  having  cementing  qualities  which  are  dependent 
mainly  on  its  bituminous  character. 

Bituminous  Concrete  Pavement,  f  One  composed  of  stone, 
gravel,  sand,  shell,  or  slag,  or  combinations  thereof,  and  bitu- 
minous materials  incorporated  together  by  mixing  methods. 

Bituminous  Macadam  Pavement.f     One  having  a  wearing 


APPENDIX  I  453 

course  of  macadam  with  the  interstices  filled  by  ^penetration 
methods  with  a  bituminous  binder. 

Bituminous  Material.!  Material  containing  bitumen  as  an 
essential  constituent. 

Liquid  Bituminous  Material,  f  J  Bituminous  material  showing 
a  penetration  at  normal  temperature  under  a  load  of  50  grams 
applied  for  i  second  of  more  than  350. 

Semi-Solid  Bituminous  Material.^  Bituminous  material 
showing  a  penetration  at  normal  temperature  under  a  load  of 
100  grams  applied  for  5  seconds  of  more  than  10,  and  under  a 
load  of  50  grams  applied  for  i  second  of  not  more  than  350. 

Solid  Bituminous  Material,  f  J  Bituminous  material  showing 
a  penetration  at  normal  temperature  under  a  load  of  100  grams 
applied  for  5  seconds  of  not  more  than  10. 

Bituminous  Pavement,  f  One  composed  of  stone,  gravel, 
sand,  shell,  or  slag,  or  combinations  thereof,  and  bituminous 
materials  incorporated  together. 

Bituminous  Surface,  f  A  superficial  coat  of  bituminous  mate- 
rial with  or  without  the  addition  of  stone  or  slag  chips,  gravel, 
sand,  or  material  of  similar  character. 

Blanket,  f     See  "Carpet." 

Bleeding.  |  The  exudation  of  bituminous  material  on  the 
roadway  surface  after  construction. 

Blown  Petroleums.  J  Semi-solid  or  solid  products  produced 
primarily  by  the  action  of  air  upon  liquid  native  bitumens  which 
are  heated  during  the  blowing  process. 

Bond.f  The  combined  action  of  inertia,  friction,  and  of  the 
forces  of  adhesion  and  cohesion  which  helps  the  separate  particles 
composing  a  crust  or  pavement  to  resist  separation  under  stress. 
Mechanical  bond  is  the  bond  produced  almost  wholly,  in  a  well- 
built  broken  stone  macadam  road,  by  the  interlocking  of  angular 
fragments  of  stone  and  the  subsequent  filling  of  the  remaining 
interstices  with  the  finer  particles. 

Bound,  f     Bonded. 

Water-Bound,  f    Bonded  with  the  aid  of  water. 

Bituminous  Bound,  f  Bonded  with  the  aid  of  bituminous 
material. 


454  ELEMENTS   OF  HIGHWAY  ENGINEERING 

Breccia.  A  rock  composed  of  angular  fragments  larger  than 
sand  grains,  cemented  together,  and  often  presenting  a  variety 
of  colors. 

Brick  Pavement,  f  One  having  a  wearing  course  of  paving 
bricks  or  blocks. 

Bridge,  f  A  structure  for  the  purpose  of  carrying  traffic  over 
a  gap  in  the  road-bed  measuring  10  feet  or  more  in  the  clear 
span. 

Camber  of  a  Bridge,  f  The  rise  of  its  center  above  a  straight 
line  through  its  ends. 

Camber  of  a  Road.f    See  "Crown." 

Carbenes.  f  J  The  components  of  the  bitumen  in  petroleums, 
petroleum  products,  malthas,  asphalt  cements,  and  solid  native 
bitumens,  which  are  soluble  in  carbon  disulphide,  but  insoluble 
in  carbon  tetrachloride. 

Carpet,  t  A  bituminous  surface  of  appreciable  thickness, 
generally  formed  on  top  of  a  roadway  by  the  application  of  one 
or  more  coats  of  bituminous  material  with  gravel,  sand,  or 
stone  chips  added. 

Cellular.  A  textural  term  used  to  describe  a  rock  structure 
containing  cells  due  to  weathering  out  of  some  constituent 

Cement,  t  An  adhesive  substance  used  for  uniting  particles 
of  other  materials  to  each  other.  Ordinarily  applied  only  to 
calcined  "cement  rock/'  or  to  artificially  prepared,  calcined,  and 
ground  mixtures  of  limestone  and  silicious  materials.  Some- 
times used  to  designate  bituminous  binder  used  in  bituminous 
pavements,  when  the  expression  "bituminous  cement"  (q.  v.)  is 
understood  to  be  meant. 

Cement-Concrete,  f  An  intimate  mixture  of  gravel,  shell, 
slag,  or  broken  stone  particles  with  certain  proportions  of  sand 
or  similar  material,  cement,  and  water,  made  previous  to 
placing. 

Cement-Concrete  Pavement,  f  One  having  a  wearing  course 
of  hydraulic  cement-concrete. 

Cemented.!  Bonded.  Referring  to  water-bound  macadam, 
the  term  "cemented"  is  used  to  designate  that  condition  existing 
when,  after  rolling  the  stone  forming  the  crust,  the  remaining 


APPENDIX  I  455 

voids  have  been  filled  with  the  finer  sizes,  and  the  stone  dust 
or  "flour"  has,  under  the  action  of  water,  taken"  a  "set,"  as 
does  cement  itself. 

Chert.  J  Compact  silicious  rock  formed  of  chalcedonic  or 
opaline  silica,  or  both. 

Chips,  f    Small  angular  fragments  of  stone  containing  no  dust. 

Clay. ft  Finely  divided  earth,  generally  silicious  and  alumi- 
nous, which  will  pass  a  2oo-mesh  sieve. 

Coal-Tar.ft  The  mixture  of  hydrocarbon  distillates,  mostly 
unsaturated  ring  comoounds,  produced  in  the  destructive  dis- 
tillation of  coal. 

Coat.f  See  "Carpet."  (i)  The  total  result  of  one  or  more 
single  surface  applications.  (2)  To  apply  a  coat. 

Coke-Oven  Tar.Jt  Coal-tar  produced  in  by-product  coke 
ovens  in  the  manufacture  of  coke  from  bituminous  coal. 

Colloidal.  A  textural  term  used  to  describe  a  jelly  or  gluelike 
rock  structure. 

Consistency. ft  The  degree  of  solidity  or  fluidity  of  bitumi- 
nous materials. 

Course,  f  One  or  more  layers  of  road  metal  spread  and  com- 
pacted separately  for  the  formation  of  the  road  or  pavement. 
Courses  are  usually  referred  to  in  the  order  of  their  laying  as 
first  course,  second  course,  third  course,  etc.  Also  a  single  row 
of  blocks  in  a  pavement. 

Crown,  f  The  rise  in  cross-section  from  the  lowest  to  the 
highest  part  of  the  finished  roadway.  It  may  be  expressed 
either  as  so  many  inches  (or  tenths  of  a  foot),  or  as  a  rate  per 
foot  of  distance  from  side  to  center,  i.  e.,  "the  crown  is  4  inches," 
or  "the  crown  is  %  inch  to  the  foot." 

Crusher  Run. ft  The  total  unscreened  product  of  a  stone 
crusher. 

Crusher-Run  Stone.  \  The  product  of  a  stone  crusher,  un- 
screened except  for  the  removal  of  the  particles  smaller  than 
remaining  on  about  a  j^-inch  screen. 

Crust,  f  That  portion  of  a  macadam  or  similar  roadway 
above  the  foundation  consisting  of  the  road  metal  proper  with 
its  bonding  agent  or  binder. 


456  ELEMENTS   OF  HIGHWAY  ENGINEERING 

Crystalline.  A  textural  term  used  to  describe  a  rock  structure 
similar  to  that  of  granite. 

Culvert,  f  A  structure  for  the  purpose  of  carrying  traffic  over 
a  gap  in  the  road-bed,  measuring  less  than  10  feet  in  clear  span. 

Cut-Back  Products.!  Petroleum,  or  tar  residuums,  which 
have  been  fluxed,  each  with  its  own  or  similar  distillates. 

Dead  Oils,  f*  Oils,  with  a  density  greater  than  water,  which 
are  distilled  from  tars. 

Dehydrated  Tars. ft  Tars  from  which  all  water  has  been 
removed. 

Diabase.  Crystalline-granular  igneous  rocks,  consisting  es- 
sentially of  plagioclase,  augite,  and  magnetite,  with  or  without 
olivine. 

Diorite.  Granitoid  rock  consisting  essentially  of  plagioclase 
and  hornblende,  with  usually  more  or  less  biotite. 

Ditch,  f  The  open-side  drain  of  a  roadway,  usually  deep  in 
proportion  to  its  width,  and  unpaved. 

Dolerite.    Coarsely  crystalline  basalts. 

Dolomite.  A  native  carbonate  of  calcium  and  magnesium, 
occurring  as  a  crystallized  mineral,  and  also  on  a  large  scale  in 
granular  crystalline  rock-masses. 

Drainage.!    Provision  for  the  disposition  of  water. 

Side- Drainage,  f    That  along  the  sides  of  the  roadway. 

Sub-  or  Under- Drainage.^    That  below  the  surface. 

Surface  Drainage,  f    That  on  the  roadway  or  ground  surface. 

V -Drainage.^  That  provided  by  the  construction  of  troughs 
in  the  subgrade  of  the  roadway,  which  troughs  are  like  a  "V," 
with  flat  sloping  sides,  and  are  filled  with  stone/ 

Dust.fJ  Earth  or  other  matter  in  fine,  dry  particles,  so 
attenuated  that  they  can  be  raised  and  carried  by  air  currents. 
The  product  of  the  crusher  passing  through  a  fine  sieve. 

Dust  Layer,  f  Material  applied  to  a  roadway  for  temporarily 
preventing  the  formation  or  dispersion  under  traffic  of  distribu- 
table dust. 

Earth  Road.f  A  roadway  composed  of  natural  earthy 
material. 

Emulsion,  f    A  combination  of  water  and  oily  material  made 


APPENDIX    I  457 

miscible  with  water  through  the  action  of  a  saponifying  or 
other  agent. 

Epidiorite.  Diabase  whose  augite  is  in  part  alter ea  to  green 
hornblende. 

Expansion  Joint,  f  A  separation  of  the  mass  of  a  structure, 
usually  in  the  form  of  a  joint  filled  with  elastic  material,  which 
will  provide  opportunity  for  slight  movement  in  the  structure. 

Fat.f  Containing  an  excess.  A  fat  asphalt  mixture  is  one 
in  which  the  asohalt  cement  is  in  excess  and  the  excess  is  clearly 
apparent. 

Felsite.  Finely  crystalline  varieties  of  quartz-porphyries,  por- 
phyries, or  porphy rites  that  have  few  or  no  phenocrysts,  and 
that,  therefore,  give  but  slight  indications  to  the  unaided  eye  of 
their  actual  mineralogical  composition. 

Filler,  ft  (i)  Relatively  fine  material  used  to  fill  the  voids 
in  the  aggregate.  (2)  Material  used  to  fill  the  joints  in  a  brick 
or  block  pavement. 

Fixed  Carbon,  y*  The  organic  matter  of  the  residual  coke 
obtained  upon  burning  hydrocarbon  products  in  a  covered  vessel 
in  the  absence  of  free  oxygen. 

Flour.  |  Finely  ground  rocks  or  minerals  pulverized  to  an 
impalpable  product. 

Flush  Coat.f    See  "Seal  Coat." 

Flushing.f  (i)  Completely  filling  the  voids.  (2)  Washing  a 
pavement  with  an  excess  of  water. 

Flux. ft  Bitumens,  generally  liquid,  used  in  combination 
with  harder  bitumens  for  the  purpose  of  softening  the  latter. 

Foliated.  A  textural  term  used  to  describe  a  rock  structure 
which  has  a  tendency  to  split  along  lines  of  stratification. 

Footway,  t  The  portion  of  the  highway  devoted  especially 
to  pedestrians.  A  sidewalk. 

Foundation.!  The  portion  of  the  roadway  below  and  sup- 
porting the  crust  or  pavement. 

Artificial  Foundation.^  That  layer  of  the  foundation  espe- 
cially placed  on  the  subgrade  for  the  purpose  of  reinforcing  the 
supporting  power  of  the  latter  itself,  and  composed  of  material 
different  from  that  of  the  subgrade  proper. 


458  ELEMENTS   OF   HIGHWAY  ENGINEERING 

Natural  Foundation.  The  natural  earthy  material  below 
and  supporting  the  artificial  foundation  or,  if  there  is  no  arti- 
ficial foundation,  the  crust  or  pavement. 

Free  Carbon,  f*  In  tars,  organic  matter  which  is  insoluble 
in  carbon  disulphide. 

Gabbro.  Igneous  rocks  of  granitoid  texture,  consisting  of 
plagioclase  and  diallage,  but  as  now  employed,  any  monoclinic 
pyroxene  may  be  present,  with  or  without  diallage. 

Gas-House  Coal-Tar. It  Coal-tar  produced  in  gas-house  re- 
torts in  the  manufacture  of  illuminating  gas  from  bituminous  coal. 

Glass.  A  textural  term  used  to  describe  an  amorphous  rock 
structure  formed  by  the  quick  chilling  of  a  fused  lava. 

Gneiss.  Laminated  or  foliated  granitoid  rock  that  corre- 
sponds in  mineralogical  composition  to  some  one  of  the  plutonic 
rocks. 

Grade,  f  (i)  The  profile  of  the  center  01  the  roadway,  or  its 
rate  of  rise  or  fall.  (2)  Elevation.  (3)  To  establish  a  profile  by 
cuts  and  fills  or  earthwork.  (4)  To  arrange  by  sizes,  broken 
stone,  gravel,  sand,  or  combinations  of  such  materials. 

Granite.J  A  granitoid  igneous  rock  consisting  of  quartz, 
orthoclase,  more  or  less  oligoclase,  biotite,  and  muscovite. 

Granitoid.  J  A  textural  term  to  describe  those  igneous  rocks 
which  are  entirely  composed  of  recognizable  minerals. 

Granular.  A  textural  term  used  to  describe  a  rock  structure 
made  up  of  distinct  grains. 

Gravel. It  Small  stones  or  pebbles  which  will  not  pass  a 
lo-mesh  sieve. 

Greywacke.  Metamorphosed,  shaly  sandstones  that  yield  a 
tough,  irregular  breaking  rock. 

Grit.{    Stone  chips,  slag  chips,  or  small  gravel 

Gutter,  f  The  artificially  surfaced  and  generally  shallow 
waterway  provided  usually  at  the  sides  of  the  roadway  for 
carrying  surface  drainage.  Occasionally  used  synonymously 
with  "ditch,"  but  incorrectly  so,  as  "gutters"  are  always  paved 
or  otherwise  surfaced,  and  ditches  are  not. 

Haunches,  f  The  sides  or  flanks  of  a  roadway.  Sometimes 
also  called  "quarters." 


APPENDIX  I  459 

Highway,  f  The  entire  right  of  way  devoted  to  public  travel, 
including  the  sidewalks  and  other  public  spaces,  if  such  exist. 

Holocrystalline.  A  textural  term  used  to  describe  a  rock 
structure  that  consists  entirely  of  crystallized  minerals. 

Hornblende  Schist.  A  schistose  rock  consisting  chiefly  of 
black  or  dark-green  hornblende,  but  often  interlaminated  with 
feldspar,  quartz,  or  mica. 

Humus.  Soil  formed  by  the  decomposition  of  vegetable 
matter  on  the  surface  of  the  ground. 

Igneous  Rocks.  Rocks  which  have  been  formed  by  mineral 
matter  flowing  upward  in  a  molten  condition  and  cooling  near 
the  surface. 

Laminated.  A  textural  term  used  to  describe  a  banded 
structure  which  is  characteristic  of  many  sedimentary  rocks. 

Layer,  f    A  course  made  in  one  application. 

Limestone.    Rock  composed  essentially  of  calcium  carbonate. 

Loam,  jt  Finely  divided  earthy  material  containing  a  con- 
siderable proportion  of  organic  matter. 

Macadam.|  A  road  crust  composed  of  stone  or  similar 
material  broken  into  irregular  angular  fragments  compacted  to- 
gether so  as  to  be  interlocked  and  mechanically  bound  to  the 
utmost  possible  extent. 

Marble.  Limestones  which  have  sufficiently  close  texture  to 
take  a  polish. 

Marl.  Calcareous  clay  containing  a  minimum  of  15  percent 
of  carbonate  of  lime  and  a  maximum  of  75  percent  of  clay. 

Massive.  A  textural  term  used  to  describe  igneous  rocks 
that  show  no  stratification. 

Mastic,  f  A  mixture  of  bituminous  material  and  fine  mineral 
matter  suitably  made  for  use  in  highway  construction  and  for 
application  in  a  heated  condition. 

Matf    See  "Carpet." 

Matrix.  {  The  binding  material  or  mixture  of  binding  mate- 
rial and  fine  aggregate  in  which  the  large  aggregate  is  embedded 
or  held  in  place.  :  * 

Mesh.f    The  square  opening  of  a  sieve. 

Metal,  f   See  "Road  Metal." 


460  ELEMENTS   OF   HIGHWAY  ENGINEERING 

Metamorphic  Rocks.  Rocks  which  have  been  changed  by 
dynamic  or  chemical  agencies  from  their  original  condition. 

Mortar,  f  A  mixture  of  fine  material  such  as  sand,  cement, 
and  water  or  other  liquid  suitably  proportioned  and  incorporated 
together  for  the  purpose  for  which  it  is  used. 

Mush.f  A  greasy  mud  sometimes  found  on  bituminous 
crusts. 

Native  Asphalt.  {    Asphalt  occurring  as  such  in  nature. 

Norite.  Rock  of  the  gabbro  family  that  consists  of  plagio- 
clase  and  orthorhombic  pyroxene,  usually  hyperosthene. 

Normal  Temperature,  ft    In  laboratory  investigations,  25°  C. 

(77°  F.). 

Oil-Gas  Tars.J  Tars  produced  by  cracking  oil  vapors  at 
high  temperatures  in  the  manufacture  of  oil-gas. 

Palliative.!    A  short-lived  dust  layer. 

Patching.!  Repairing  or  restoring  small  isolated  areas  in 
the  surface  of  the  metaled  or  paved  portion  of  the  highway. 

Pavement,  f  The  wearing  course  of  the  roadway  or  footway, 
when  constructed  with  a  cement  or  bituminous  binder,  or  com- 
posed of  blocks  or  slabs,  together  with  any  cushion  or  "binder" 
course. 

Peat.  Soil  formed  by  the  decomposition  of  vegetable  matter 
under  water. 

Pegmatite.  Very  coarse  granites,  such  as  have  large  quartz, 
feldspar,  muscovite,  biotite,  tourmaline,  beryl,  and  other  char- 
acteristic minerals. 

Penetration.f  In  laboratory  investigations,  the  distance,  ex- 
pressed in  tenths  of  a  millimeter,  entered  a  sample  by  a  No.  2 
cambric  needle  operated  in  a  machine  for  the  purpose  and  under 
known  conditions  of  loading,  time,  and  temperature.  The  degree 
of  solidity  of  bituminous  materials. 

In  construction,  the  entrance  of  bituminous  material  into 
the  interstices  of  the  metal  of  the  roadway. 

Penetration  Method,  f  The  method  of  constructing  a  bitu- 
minous macadam  pavement  by  pouring  or  grouting  the  bitumi- 
nous material  into  the  upper  course  of  the  road  metal  before 
the  binding  of  the  latter  has  been  completed. 


APPENDIX  I  461 

Petroleum.  A  natural  rock  oil  composed  of  hydrocarbons. 
(The  New  International  Encyclopaedia.) 

Pitch. ft  Solid  residue  produced  in  the  evaporation  or  dis- 
tillation of  bitumens,  the  term  being  usually  applied  to  residue 
obtained  from  tar. 

Hard  Pitch,  f  Pitch  showing  a  penetration  of  not  more  than 
ten. 

Soft  Pitch,  !    Pitch  showing  a  penetration  of  more  than  ten. 

Plutonic  Rocks.  Rocks  which  were  formed  by  the  cooling  of 
molten  mineral  matter  before  it  reached  the  surface. 

Pocket,  f    A  hole  or  depression  in  the  wearing  course. 

Porphyritic.  A  textural  term  used  to  describe  a  compact 
structure  throughout  which  there  are  large  crystals. 

Porphyry.  Rock  consisting  of  a  very  fine-grained  or  micro- 
crystalline  ground-mass  through  which  are  disseminated  dis- 
tinctly recognizable  crystals  of  some  mineral. 

Pot-Hole.f    A  hole  extending  below  the  wearing  course. 

Profile.!  A  longitudinal  section  of  a  highway,  generally 
taken  along  the  center  line. 

Quarters.  |  The  four  sections  of  equal  width  which,  side  by 
side,  make  up  the  total  width  of  a  roadway. 

Raveling,  f  The  loosening  of  the  metal  composing  the 
crust. 

Refined  Tar.fJ  A  tar  freed  from  water  by  evaporation  or 
distillation  which  is  continued  until  the  residue  is  of  desired 
consistency,  or  a  product  produced  by  fluxing  tar  residuum  with 
tar  distillate. 

Renewals.f  Extensive  repairs  over  practically  the  whole 
surface  of  the  metaled  or  paved  portion  of  the  highway. 

Repairs.f  The  restoration  or  mending  of  a  considerable 
amount  of  the  metaled  or  paved  portion  of  the  highway,  but  not 
usually  of  a  majority  of  the  surface  area.  More  extensive  than 
"Patching"  but  less  so  than  "Renewals." 

Resurfacing.!  The  renewal  of  the  surface  of  the  crust  or 
pavement. 

Rhyolite.  Volcanic  rocks  of  porphyritic  or  felsitic  texture, 
whose  phenocrysts  are  prevailingly  orthoclase  and  quartz,  less 


462  ELEMENTS   OF   HIGHWAY  ENGINEERING 

abundantly  biotite,  hornblende,  or  pyroxene,  and  whose  ground- 
mass  is  crystalline,  glassy,  or  both. 

Road.f    A  highway  outside  of  an  urban  district. 

Road-Bed.j    The  natural  foundation  of  a  roadway. 

Road  Metal,  f  Broken  stone,  gravel,  slag,  or  similar  material 
used  in  road  and  pavement  construction  and  maintenance. 

Roadway,  f  That  portion  of  a  highway  particularly  devoted 
to  the  use  of  vehicles. 

Rock  Asphalt.  |  Sandstone  or  limestone  naturally  impreg- 
nated with  asphalt. 

Rock  Asphalt  Pavement,  f  A  wearing  course  composed  of 
broken  or  pulverized  rock  asphalt  with  or  without  the  addition 
of  other  bituminous  materials. 

Rubble.  J  Rough  stones  of  irregular  shapes  and  sizes,  broken 
from  larger  masses,  either  naturally  or  artifically,  as  by  geological 
action,  in  quarrying,  or  in  stone-cutting  or  blasting. 

Sand.  tJ  Finely  divided  rock  detritus  the  particles  of  which 
will  pass  a  lo-mesh  and  be  retained  on  a  2oo-mesh  screen. 

Sand-Clay  Road,  f  A  roadway  composed  of  an  intimate  mix- 
ture of  sand  and  clay. 

Sandstone.    Rock  formed  by  the  consolidation  of  sand. 

Scarify.!    To  loosen  and  disturb  superficially. 

Schist.  Thinly  laminated,  metamorphic  rocks  which  split 
more  or  less  readily  along  certain  planes  approximately  parallel 
and  differing  from  the  gneisses  principally  in  the  lack  of  feldspar. 

Schistose.  A  textural  term  used  to  describe  a  rock  structure 
which  has  a  tendency  to  split  along  lines  of  stratification. 

Screen,  ft  In  laboratory  work  an  apparatus,  in  which  the 
apertures  are  circular,  for  separating  sizes  of  material. 

Screenings.  J  Broken  rock,  including  the  dust,  of  a  size  that 
will  pass  through  a  y2-  to  ^-inch  screen,  depending  upon  the 
character  of  the  stone. 

Seal  Coat.f  A  final  superficial  application  of  bituminous 
material  during  construction  to  a  bituminous  pavement. 

Setting  Up.f  The  relatively  quick  change  such  as  takes 
place  in  a  bituminous  material  after  its  application  to  a  roadway, 
indicated  by  its  hardening  after  cooling  and  exposure  to  atmos- 


APPENDIX  I  463 

pheric  and  traffic  conditions,  as  opposed  to  the  slower  changes 
later  occurring  gradually  and  almost  imperceptibly. ' 

Shaping,  f  Trimming  up  and  preparing  a  subgrade  prepara- 
tory to  applying  the  first  course  of  the  road  metal  or  artificial 
foundation. 

Sheet  Asphalt  Pavement,  f  One  having  a  wearing  course 
composed  of  asphalt  cement  and  sand  of  predetermined  grading, 
with  or  without  the  addition  of  fine  material,  incorporated  to- 
gether by  mixing  methods. 

Sheet  Pavement,  f  A  pavement  free  from  frequent  joints 
such  as  would  accompany  small  slabs  or  blocks,  and  which  has 
an  appreciable  thickness  (say,  in  excess  of  i  inch  on  the  average) 
for  its  wearing  course. 

Shoulders,  f  The  portion  of  the  highway  between  the  edges 
of  the  road*  metal  or  pavement  and  the  gutters,  slopes,  or  water- 
courses. 

Side  Drain. f    See  "Drainage." 

Sidewalk,  f  The  portion  of  the  highway  reserved  for  pedes- 
trians. 

Sieve.  |  In  laboratory  work  an  apparatus  in  which  the  aper- 
tures are  square,  for  separating  sizes  of  material. 

Silt.ft  Naturally  deposited  fine  earthy  material,  which  will 
pass  a  2oo-mesh  sieve. 

Slag.  Fused  compounds  of  silica  in  combination  with  lime 
or  other  bases,  resulting  as  secondary  products  from  the  reduc- 
tion of  metallic  ores.  (New  International  Encyclopaedia.) 

Soil.J  A  mixture  of  fine  earthy  material,  with  more  or  less 
organic  matter,  resulting  from  the  growth  and  decomposition  of 
vegetable  or  animal  matter. 

Spalls.|  Fragments  broken  off  by  a  blow,  irregular  in  shape, 
and  of  sufficient  size  to  be  comparable  to  the  original  mass. 

Squeegee.f  A  tool  with  a  rubber  or  leather  edge  for  scraping 
or  cleaning  hard  surfaces,  or  for  spreading  and  distributing  liquid 
material  over  and  into  the  superficial  interstices  of  roadways. 
Squeegee  Coat.f  An  application  by  means  of  the  squeegee. 
Stone  Block  Pavement.f  One  having  a  wearing  course  com- 
posed of  stone  blocks  quite  or  nearly  rectangular  in  shape. 


464  ELEMENTS   OF   HIGHWAY  ENGINEERING 

Stone  Chips.  {  Small  angular  fragments  of  stone  containing 
no  dust. 

Straight-Run  Pitch. }  A  pitch  run  to  the  consistency  desired, 
in  the  initial  process  of  distillation,  without  subsequent  fluxing. 

Stratified.  A  textural  term  used  to  describe  a  rock  structure 
composed  of  parallel  layers. 

Street,  f    A  highway  in  an  urban  district. 

Subgrade.f  The  upper  surface  of  the  native  foundation 
on  which  is  placed  the  road  metal  or  the  artificial  foundation, 
in  case  the  latter  is  provided. 

Superficial  Coat.f    A  light  surface  coat. 

Surface  Coat.f    See  "Carpet." 

Surface  Treatment,  f  Treating  the  finished  surface  of  a  road- 
way with  bituminous  material. 

Surfacing.!  (i)  The  crust  or  pavement.  (2)  Constructing  a 
crust  or  pavement.  (3)  Finally  finishing  the  surface  of  a  road- 
way. (4)  Treating  the  surface  of  a  finished  roadway  with  a 
bituminous  material. 

Syenite.  Granitoid  rocks  consisting  of  orthoclase,  hornblende, 
biotite,  and  augite. 

Tailings.fi  Stones,  which  after  going  through  the  crusher, 
do  not  pass  through  the  largest  openings  of  the  screen. 

Tar.Jt  Bitumen  which  yields  pitch  upon  fractional  distil- 
lation and  which  is  produced  as  a  distillate  by  the  destructive 
distillation  of  bitumens,  pyro-bitumens,  or  organic  material. 

Telford.  f  Properly,  an  artificial  foundation  advocated  by 
Thomas  Telford  (1757-1820),  and  consisting  of  a  pavement  of 
stone  about  8  inches  thick,  laid  by  hand,  and  closely  packed  and 
wedged  together.  The  individual  stones  were  desired  to  be  about 
1 6  square  inches  in  section,  and  about  8  inches  in  length.  They 
were  set  close  together  on  the  prepared  subgrade,  their  longest 
dimension  vertical  and  on  their  larger  ends,  their  interstices 
chinked  with  smaller  stones,  and  the  whole  rammed  (or  rolled) 
until  firm  and  unyielding. 

Telford  Macadam.  |  Macadam  with  an  artificial  foundation 
of  Telford. 

Trap  Rock.    A  very  general  term,  little  employed  in  scien- 


APPENDIX  I  465 

tific  language  but  commonly  used  to  designate  dense  and  gener- 
ally fine-grained  igneous  rocks  of  black  or  dark-green  color. 
The  term  is  almost  synonymous  with  basalt  or  diabase  but 
might  include  as  well,  gabbro,  norite,  peridotite,  pyroxenite,  etc. 
When  altered  such  rocks  assume  a  green  color  from  hornblende, 
chlorite,  epidote,  or  other  secondary  minerals  developed  in  them, 
and  they  are  then  known  as  greenstone.  Both  greenstone  and 
trap  would  include  a  wide  range  of  rock  families  which  by 
reason  of  their  fine  texture  and  altered  condition  are  difficult 
to  determine  without  careful  and  generally  microscopic  study. 
(The  New  International  Encyclopaedia.) 

Under-Drain.f    See  "Drainage." 

Up-Keep.  f    Maintenance. 

V-Drain.f     See  "Drainage." 

Viscosity.j    The  degree  of  fluidity  of  bituminous  materials. 

Volatile.!  Applied  to  those  fractions  of  bituminous  materials 
which  will  evaporate  at  climatic  temperatures. 

Volcanic  Rocks.  Rocks  which  have  been  formed  by  mineral 
matter  erupted  in  a  molten  condition  and  cooled  on  the  surface. 

Water-Bound.!    Bound  or  bonded  with  the  aid  of  water. 

Water-Gas  Tars.J  Tars  produced  by  cracking  oil  vapors  at 
high  temperatures  in  the  manufacture  of  carburetted  water-gas. 

Wearing  Coat.!  The  superficial  layer  of  the  crust  or  pave- 
ment exposed  to  traffic. 

Wearing  Course.!  The  course  of  the  crust  or  pavement  ex- 
posed to  traffic. 

Wood  Block  Pavement,  f  One  having  a  wearing  course  com- 
posed of  wood  paving  blocks,  generally  rectangular  in  shape. 


APPENDIX  II 
TESTS  OF  BITUMINOUS  MATERIALS 

The  following  methods*  for  performing  tests  to  determine 
the  several  chemical  and  physical  properties  of  bituminous  mate- 
rials were  recommended  for  adoption  by  the  Special  Committee 
on  "Materials  for  Road  Construction"  at  the  1915  Annual 
Meeting  of  the  American  Society  of  Civil  Engineers.  It  will 
be  noted  that  some  of  these  methods  were  originally  proposed 
by  Sub-Committees  of  Committee  D-4  on  "Standard  Tests  for 
Road  Materials"  of  the  American  Society  for  Testing  Materials. 

SPECIFIC  GRAVITY 

For  liquid  and  semi-solid  materials,  some  standard  form  of 
pyknometer  shall  be  used.  For  solid  materials,  the  suspension 
method  shall  be  used.  Material  and  distilled  water  shall  have  a 
temperature  of  25°  Cent.  (77°  Fahr.). 

The  pyknometer  to  be  used  shall  consist  of  a  fairly  heavy, 
straight- walled  glass  tube,  70  mm.  (2.75  inch)  long  and  22  mm. 
(0.875  inch)  in  diameter,  ground  to  receive  a  solid  glass  stopper 
with  a  hole  of  i.6-mm.  (o.o63-inch)  bore,  in  place  of  the  usual 
capillary  opening.  The  lower  part  of  this  stopper  shall  be  made 
concave  in  order  to  allow  all  air  bubbles  to  escape  through  the 
bore.  The  depth  of  the  cup-shaped  depression  is  4.8  mm. 
(0.188  inch)  at  the  center.  The  stoppered  tube  shall  have  a 
capacity  of  about  24  cu.  cm.  (0.8 n  ounce)  and  when  empty  shall 
weigh  about  28  grams.  Its  principal  advantages  are:  (i) 
that  any  desired  quantity  of  bituminous  material  may  be  poured 
in  without  touching  the  sides  above  the  level  desired;  (2)  it  is 
easily  cleaned;  (3)  on  account  of  the  i.6-mm.  (o.o63-inch)  bore, 
the  stopper  can  be  more  easily  inserted  when  the  tube  is  filled 

*Dec.,  1914  Proceedings,  American  Society  of  Civil  Engineers,  pages  3036-3050. 

466 


APPENDIX  n  467 

with  a  very  viscous  oil  than  if  it  contained  a  capillary  opening. 
When  testing  solid  or  semi-solid  materials  with  the  pyknometer, 
extreme  care  should  be  taken  in  melting,  to  avoid  loss  by  evap- 
oration, and,  in  filling  the  pyknometer,  to  avoid  entrapping  air. 
When  working  with  semi-solid  bituminous  materials  which  are 
too  soft  to  be  broken  and  handled  in  fragments,  the  following 
method  of  determining  their  specific  gravity  has  been  used  with 
good  results.  The  clean,  dry  pyknometer  is  first  weighed  empty 
and  this  weight  is  called  a.  It  is  then  filled  in  the  usual  manner 
with  freshly  distilled  water  at  25°  Cent.  (77°  Fahr.),  and  the 
weight  is  again  taken  and  called  b.  A  small  quantity  of  the  ma- 
terial is  then  placed  in  a  spoon  and  brought  to  a  fluid  condition 
by  the  gentle  application  of  heat,  with  care  that  no  loss  by  evap- 
oration occurs.  When  sufficiently  fluid,  enough  is  poured  into 
the  dry  pyknometer,  which  may  also  be  warmed,  to  fill  it  about 
half  full,  without  allowing  the  material  to  touch  the  sides  of  the 
tube  above  the  desired  level.  The  tube  and  contents  are  then 
allowed  to  cool  to  room  temperature,  after  which  the  tube  is 
carefully  weighed  with  the  stopper.  This  weight  is  called  c. 
Distilled  water,  at  25°  Cent.  (77°  Fahr.),  is  then  poured  in  until 
the  pyknometer  is  full.  After  this  the  stopper  is  inserted  and  the 
whole  is  cooled  to  25°  Cent.  (77°  Fahr.)  by  a  30-minute  im- 
mersion in  a  beaker  of  distilled  water  maintained  at  this  tem- 
perature. All  surplus  moisture  is  then  removed  with  a  soft  cloth, 
and  the  pyknometer  and  contents  are  weighed.  This  weight  is 
called  d.  From  the  weights  obtained,  the  specific  gravity  of  the 
material  may  be  readily  calculated  by  the  following  formula: 

Specific  gravity  25°  Cent.  (77°  Fahr.)/  25°  Cent.  (77°  Fahr.) 


(b-a)-(d-c) 

Both  a  and  b  are  constants,  and  need  be  determined  only  once. 
It  is  necessary,  therefore,  to  make  only  two  weighings  for  each 
determination  after  the  first.  Results  obtained  according  to  this 
method  are  accurate  to  within  two  units  in  the  third  decimal 
place,  whereas  the  open-tube  method  commonly  used  is  accurate 
to  the  second  decimal  place  only. 


468  ELEMENTS   OF   HIGHWAY   ENGINEERING 

The  specific  gravity  of  fluid  bituminous  material  may  be  de- 
termined in  the  ordinary  manner  with  this  pyknometer  by  com- 
pletely filling  it  with  the  material  and  dividing  the  weight  of  the 
bituminous  material  thus  obtained  by  that  of  the  same  volume 
of  water. 

FLASH  POINT 

The  flash  point  shall  be  determined  by  the  closed-cup  test. 

Although  for  ordinary  purposes,  the  open-cup  method  of 
determining  the  flash  and  burning  points  of  bituminous  materials 
is  reasonably  accurate,  the  closed-cup  method  described  below  is 
to  be  preferred. 

The  oil  tester  shall  consist  of  a  copper  oil  cup  having  a  capacity 
of  about  300  cu.  cm.  (10.1  ounce),  and  shall  be  heated  in  a  water  or 
oil  bath  by  a  small  Bunsen  flame.  The  cup  shall  be  provided 
with  a  glass  cover,  carrying  a  thermometer,  and  a  hole  for  in- 
serting the  testing  flame.  The  testing  flame  shall  be  obtained 
from  a  jet  of  gas  passed  through  the  piece  of  glass  tubing,  and 
shall  be  about  5  mm.  (0.197  inch)  in  length. 

The  flash  test  shall  be  made  as  follows :  The  oil  cup  shall  first 
be  removed  and  the  bath  filled  with  water  or  cottonseed  oil. 
The  oil  may  always  be  used,  and  is  necessary  for  bituminous 
material  flashing  at  a  temperature  of  more  than  100°  Cent. 
(212°  Fahr.).  The  oil  cup  shall  be  replaced  and  filled  with  the 
material  to  be  tested  to  within  3  mm.  (0.118  inch)  of  the  flange 
joining  the  cup  and  the  vapor  chamber  above.  The  glass  cover 
shall  then  be  placed  on  the  oil  cup  and  the  thermometer  adjusted 
so  that  its  bulk  shall  be  just  covered  by  the  bituminous  material. 
The  Bunsen  flame  shall  be  applied  in  such  a  manner  that  the 
temperature  of  the  material  in  the  cup  shall  be  raised  at  the  rate 
of  about  5°  Cent.  (9°  Fahr.)  per  minute.  From  time  to  time  the 
testing  flame  shall  be  inserted  in  the  opening  in  the  cover  to  about 
half  way  between  the  surface  of  the  material  and  the  cover. 
The  appearance  of  a  faint  bluish  flame  over  the  entire  surface 
of  the  bituminous  material  will  show  that  the  flash  point  has  been 
reached  and  the  temperature  at  this  point  is  taken. 


APPENDIX   II  469 

SOLUBILITY  IN  CARBON  BISULPHIDE  (€82) 

This  test  shall  consist  in  dissolving  the  bituminous  material 
in  carbon  disulphide  and  recovering  any  insoluble  matter  by 
filtering  the  solution  through  an  asbestos  felt.  The  Gooch 
crucible  used  for  the  determination  shall  be  4.4  cm.  (1.722  inch) 
wide  at  the  top,  tapering  to  3.6  cm.  (1.417  inch)  at  the  bottom, 
and  shall  be  2.5  cm.  (0.984  inch)  deep. 

The  asbestos  shall  be  cut  with  scissors  into  pieces  not  ex- 
ceeding i  cm.  (0.394  inch)  in  length,  after  which  it  shall  be  shaken 
up  with  just  sufficient  water  to  pour  easily.  The  crucible  shall  be 
filled  with  the  suspended  asbestos  and  allowed  to  settle  for  a  few 
moments.  A  light  suction  shall  then  be  applied  to  draw  off  all 
the  water  and  leave  a  firm  mat  of  asbestos  in  the  crucible.  More 
of  the  suspended  material  shall  be  added,  and  the  operation  shall 
be  repeated  until  the  felt  shall  be  so  dense  that  it  scarcely  trans- 
mits light  when  held  so  that  the  bottom  of  the  crucible  is  between 
the  eye  and  the  source  of  light.  The  felt  shall  then  be  washed 
several  times  with  water,  and  drawn  firmly  against  the  bottom 
of  the  crucible  by  an  increased  suction.  The  crucible  shall  be 
removed  to  a  drying  oven  for  a  few  minutes,  after  which  it  shall 
be  ignited  at  red  heat  over  a  Bunsen  burner,  cooled  in  a  desiccator 
and  weighed. 

Two  grams  of  bituminous  material  or  10  grams  of  an  as- 
phalt topping  or  rock  asphalt  shall  then  be  placed  in  an  Erlen- 
meyer  flask,  which  shall  have  been  weighed  previously,  and  the 
accurate  weight  of  the  sample  obtained.  One  hundred  cubic 
centimeters  (3.381  ounces)  of  chemically  pure  carbon  disulphide 
shall  be  poured  into  the  flask,  in  small  portions,  with  continual 
agitation,  until  all  lumps  disappear  and  nothing  adheres  to  the 
bottom.  The  flask  shall  then  be  corked  and  set  aside  for  15 
minutes  to  allow  settlement  of  the  insoluble  material. 

The  weighed  Gooch  crucible  containing  the  felt  shall  be  set  up 
over  the  dry  pressure  flask,  and  the  solution  of  bituminous  ma- 
terial in  carbon  disulphide  shall  be  decanted  through  the  felt 
without  suction  by  gradually  tilting  the  flask,  with  care  not  to 
stir  up  any  precipitate  that  may  have  settled  out.  At  the  first 


470  ELEMENTS   OF   HIGHWAY  ENGINEERING 

sign  of  any  sediment  coming  out,  the  decantation  shall  be  stopped 
and  the  filter  allowed  to  drain.  A  small  quantity  of  carbon  di- 
sulphide  shall  then  be  washed  down  the  sides  of  the  flask,  after 
which  the  precipitate  shall  be  brought  upon  the  felt  and  the  flask 
scrubbed,  if  necessary,  with  a  feather  or  " policeman,"  to  remove 
all  adhering  material.  The  contents  of  the  crucible  shall  be 
washed  with  carbon  disulphide  until  the  washings  run  colorless. 
Suction  shall  then  be  applied  until  there  is  practically  no  odor 
of  carbon  disulphide  in  the  crucible,  after  which  the  outside  of 
the  crucible  shall  be  cleaned  with  a  small  quantity  of  the  solvent. 
The  crucible  and  contents  shall  be  dried  in  the  hot  air  oven  at 
100°  Cent.  (212°  Fahr.)  for  about  20  minutes,  cooled  in  a  desic- 
cator, and  weighed.  If  any  appreciable  quantity  of  insoluble 
matter  adheres  to  the  flask,  it  shall  also  be  dried  and  weighed,  and 
any  increase  over  the  original  weight  of  the  flask  shall  be  added 
the  weight  of  insoluble  matter  in  the  crucible.  The  total  weight 
of  insoluble  material  may  include  both  organic  and  mineral 
matter.  The  former,  if  present,  shall  be  burned  off  by  ignition 
at  a  red  heat  until  no  incandescent  particles  remain,  thus  leaving 
the  mineral  matter  or  ash,  which  can  be  weighed  on  cooling. 
The  difference  between  the  total  weight  of  material  insoluble 
in  carbon  disulphide  and  the  weight  of  substance  taken  equals 
the  total  bitumen,  and  the  percentage  weights  are  calculated  and 
reported  as  total  bitumen,  and  insoluble  organic  and  inorganic 
matter,  on  the  basis  of  the  weight  of  material  taken  for  analysis. 
This  method  is  quite  satisfactory  for  straight  oil  and  tar 
products,  but,  where  native  asphalts  are  present,  it  will  be  found 
practically  impossible  to  retain  all  the  finely  divided  mineral 
matter  on  an  asbestos  felt.  It  is  generally  more  accurate,  there- 
fore, to  obtain  the  result  for  total  mineral  matter  by  direct  igni- 
tion of  a  i -gram  sample  in  a  platinum  crucible,  or  to  use  the 
result  for  ash  obtained  in  the  fixed  carbon  test.  The  total 
bitumen  is  then  determined  by  deducting  from  100  percent  the 
sum  of  the  percentages  of  total  mineral  matter  and  insoluble 
organic  matter.  If  the  presence  of  a  carbonate  mineral  is  sus- 
pected, the  percentage  of  mineral  matter  may  be  most  accurately 
obtained  by  treating  the  ash  from  the  fixed  carbon  determination 


APPENDIX   II  471 

with  a  few  drops  of  ammonium  carbonate  solution,  drying  at  100° 
Cent.  (212°  Fahr.),  then  heating  for  a  few  minutes  at  a  dull  red 
heat,  cooling,  and  weighing  again.  t 

When  difficulty  in  filtering  is  experienced — for  instance, 
when  Trinidad  asphalt  is  present  in  any  quantity — a  longer 
period  of  subsidence  than  15  minutes  is  necessary,  and  the 
following  method,  proposed  by  the  Committee  on  Standard  Tests 
for  Road  Materials  (Committee  D-4)  of  the  American  Society  for 
Testing  Materials,  is  recommended:  (Note:  English  equivalents 
in  brackets  have  been  added  by  the  Special  Committee  on 
Materials  for  Road  Construction.) 

From  2  to  15  grams  (depending  on  the  richness  in  bitumen 
of  the  substance)  is  weighed  into  a  150-01.  cm.  (5.072  ounces) 
Erlenmeyer  flask,  the  tare  of  which  has  been  previously  ascer- 
tained, and  treated  with  100  cu.  cm.  (3.381  ounces)  of  carbon 
disulphide.  The  flask  is  then  loosely  corked  and  shaken  from 
time  to  time  until  practically  all  large  particles  of  the  material 
have  been  broken  up,  when  it  is  set  aside  and  not  disturbed  for 
48  hours.  The  solution  is  then  decanted  off  into  a  similar  flask 
that  has  been  previously  weighed,  as  much  of  the  solvent  being 
poured  off  as  possible  without  disturbing  the  residue.  The  first 
flask  is  again  treated  with  fresh  carbon  disulphide  and  shaken 
as  before,  when  it  is  put  away  with  the  second  flask  and  not  dis- 
turbed for  48  hours. 

At  the  end  of  this  time  the  contents  of  the  two  flasks  are 
carefully  decanted  off  upon  a  weighed  Gooch  crucible  fitted  with 
an  asbestos  filter,  the  contents  of  the  second  flask  being  passed 
through  the  filter  first.  The  asbestos  filter  shall  be  made  of 
ignited  long-fibre  amphibole,  packed  in  the  bottom  of  a  Gooch 
crucible  to  the  depth  of  not  more  than  j/i  inch.  After  passing 
the  contents  of  both  flasks  through  the  filter,  the  two  residues  are 
shaken  with  more  fresh  carbon  disulphide  and  set  aside  for  24 
hours  without  disturbing,  or  until  it  is  seen  that  a  good  subsida- 
tion  has  taken  place,  when  the  solvent  is  again  decanted  off 
upon  the  filter.  This  washing  is  continued  until  the  filtrate  or 
washings  are  practically  colorless. 

The  crucible  and  both  flasks  are  then  dried  at  125°  Cent. 


472  ELEMENTS   OF   HIGHWAY   ENGINEERING 

(257°  Fahr.)  and  weighed.  The  filtrate  containing  the  bitumen 
is  evaporated,  the  bituminous  residue  burned,  and  the  weight 
of  the  ash  thus  obtained  added  to  that  of  the  residue  in  the  two 
flasks  and  the  crucible.  The  sum  of  these  weights  deducted 
from  the  weight  of  substance  taken  gives  the  weight  of  bitumen 
extracted. 


SOLUBILITY  OF  BITUMEN  IN  CARBON  TETRACHLOREDE  (CC14) 

The  test  shall  be  conducted  in  exactly  the  same  manner  as  de- 
scribed for  the  test  for  "Solubility  in  Carbon  Bisulphide, "  except 
that  100  cu.  cm.  (3.381  ounces)  of  chemically  pure  carbon 
tetrachloride  shall  be  used  in  place  of  carbon  disulphide,  and  the 
percentage  of  bitumen  insoluble  in  carbon  tetrachloride  shall  be 
reported  on  the  basis  of  the  bitumen  taken  as  100,  the  quantity 
of  bitumen  having  been  determined  by  the  method  described 
under  the  heading  "Solubility  in  Carbon  Disulphide." 

CONSISTENCY 

The  "Engler  Viscosimeter,"  the  "New  York  Testing  Labora- 
tory Float,"  or  the  "Penetrometer,"  shall  be  used,  as  practicable, 
at  4°  Cent.  (39°  Fahr.),  25°  Cent.  (77°  Fahr.),  46°  Cent.  (115° 
Fahr.),  and  98°  Cent.  (208°  Fahr.). 


VISCOSITY  TEST 

The  viscosity  of  liquid  bituminous  materials  shall  be  de- 
termined at  any  desired  temperature  by  using  the  "Engler 
Viscosimeter."  This  apparatus  consists  of  a  brass  vessel  for  hold- 
ing the  material  to  be  tested,  and  is  closed  by  a  cover.  To  the 
conical  bottom  is  fitted  a  conical  outflow  tube  exactly  20  mm. 
(0.787  inch)  long,  with  a  diameter  of  2.9  mm.  (0.114  inch)  on  top, 
and  of  2.8  mm.  (o.no  inch)  on  the  bottom.  This  tube  is  closed 
and  opened  by  a  pointed  hardwood  stopper.  Pointed  metal  pro- 
jections are  placed  on  the  inside  of  the  vessel  at  equal  distances 
from  the  bottom,  and  serve  for  measuring  the  charge  of  material, 


APPENDIX   II  473 

which  is  240  cu.  cm.  (8.116  ounces).  A  thermometer  is  used  to 
ascertain  the  temperature  of  the  material  to  be  tested.  The 
vessel  is  surrounded  by  a  brass  jacket,  which  holds  the  material 
which  may  be  used  as  a  heating  bath,  either  water  or  cottonseed 
oil,  according  to  the  temperature  at  which  the  test  is  to  be  made. 
A  tripod  serves  as  a  support  for  the  apparatus,  and  also  carries 
a  ring  burner  by  which  the  bath  is  heated  directly.  The  mea- 
suring cylinder,  having  a  capacity  of  100  cu.  cm.  (3.381  ounces), 
which  is  sufficiently  accurate  for  work  with  road  materials,  is 
placed  directly  under  the  outflow  tube. 

As  all  viscosity  determinations  should  be  compared  with  that 
of  water  at  25°  Cent.  (77°  Fahr.),  the  apparatus  shall  have  been 
previously  calibrated  as  follows:  The  cup  and  outlet  tube  shall 
first  be  scrupulously  cleaned.  A  piece  of  soft  tissue  paper  is 
convenient  for  cleaning  the  tube.  The  stopper  shall  then  be 
inserted  in  the  tube,  and  the  cup  shall  be  filled  with  water  at  25° 
Cent.  (77°  Fahr.)  to  the  top  of  the  projections.  The  measuring 
cylinder  shall  be  placed  directly  under  the  outflow  tube  so  that 
the  material,  on  flowing  out,  will  not  touch  the  sides.  The  stop- 
per shall  then  be  removed  and  the  time  required,  both  for  50  and 
100  cu.  cm.  (1.691  and  3.381  ounces)  to  run  out,  shall  be  ascer- 
tained by  using  a  stop-watch.  The  results  thus  obtained  shall 
be  checked  a  number  of  times.  The  time  required  for  50  cu. 
cm.  (1.691  ounces)  of  water  should  be  about  n  seconds  and  for 
100  cu.  cm.  (3.381  ounces)  about  22.8  seconds. 

Bituminous  materials  shall  be  tested  in  the  same  manner  as 
water,  and  the  temperature  at  which  the  test  is  made  shall  be 
controlled  by  the  bath.  The  material  shall  be  brought  to  the 
desired  temperature  and  maintained  there  for  at  least  3  minutes 
before  making  the  test.  The  results  are  expressed  as  specific 
viscosity  compared  with  water  at  25°  Cent.  (77°  Fahr.),  as  follows: 

Specific  viscosity  at degrees  centigrade  for  -    -  cu.  cm. 

equals 

seconds  for  passage  of  given  volume  at  —    —  degrees  centigrade 
seconds  for  passage  of  same  volume  of  water. 


474  ELEMENTS  OF  HIGHWAY  ENGINEERING 

FLOAT  TEST 

The  float  apparatus  consists  of  two  parts,  an  aluminum  float 
or  saucer  and  a  conical  brass  collar.  The  two  parts  are  made 
separately,  so  that  one  float  may  be  used  with  a  number  of  brass 
collars. 

In  making  the  test,  the  brass  collar  shall  be  placed  with  the 
small  end  down  on  the  brass  plate,  which  shall  have  been  pre- 
viously amalgamated  with  mercury  by  rubbing  it  first  with  a 
dilute  solution  of  mercuric  chloride  or  nitrate  and  then  with 
mercury.  A  small  quantity  of  the  material  to  be  tested  shall  be 
heated  in  the  metal  spoon  until  quite  fluid,  with  care  that  it  shall 
suffer  no  appreciable  loss  by  volatilization  and  that  it  shall 
be  kept  free  from  air  bubbles.  It  shall  then  be  poured  into  the 
collar  in  a  thin  stream  until  slightly  more  than  level  with  the  top. 
After  the  material  has  cooled  to  room  temperature,  the  surplus 
may  be  removed  with  a  spatula  blade  which  has  been  slightly 
heated.  The  collar  and  plate  shall  then  be  placed  in  one  of  the 
tin  cups  containing  ice  water  maintained  at  5°  Cent.  (41°  Fahr.), 
and  left  in  this  bath  for  15  minutes.  Meanwhile,  the  other 
cup  shall  be  filled  about  three-fourths  full  of  water  and  placed  on 
the  tripod,  and  the  water  shall  be  heated  to  any  temperature 
desired  for  the  test.  This  temperature  shall  be  accurately  main- 
tained, and  shall  at  no  time  throughout  the  entire  test  be  allowed 
to  vary  more  than  0.5°  Cent.  (0.9°  Fahr.)  from  the  temperature 
selected.  After  the  material  to  be  tested  has  been  kept  in  the 
ice  water  for  15  minutes,  the  collar  and  contents  shall  be  re- 
moved from  the  plate  and  screwed  into  the  aluminum  float, 
which  shall  then  be  immediately  floated  in  the  warmed  bath. 
As  the  plug  of  bituminous  material  becomes  warm  and  fluid, 
it  is  gradually  forced  upward  and  out  of  the  collar,  until  water 
gains  entrance  to  the  saucer  and  causes  it  to  sink. 

The  time,  in  seconds,  between  placing  the  apparatus  on  the 
water  and  when  the  float  sinks  shall  be  taken  as  a  measure  of  the 
consistency  of  the  material  under  examination. 


APPENDIX   II  475 

PENETRATION  TEST 

The  penetration  test  for  determining  the  consistency  of  a  ma- 
terial shall  be  made  by  measuring  the  distance  a  weighted 
needle  will  penetrate  into  the  material  at  a  given  temperature. 
A  standard  No.  2  cambric  needle,  weighted  with  100  grams, 
shall  be  used,  except  as  noted  below,  and  the  depth  of  penetra- 
tion shall  be  determined  on  the  bituminous  material  maintained 
at  25°  Cent.  (77°  Fahr.)  while  the  load  is  applied  for  5  seconds. 
When  the  penetration  test,  made  as  above  described,  will  give  a 
result  of  less  than  10  or  more  than  350,  the  loading  and  time  shall 
be  changed  to  200  grams  for  i  minute,  and  50  grams  for  5 
seconds,  respectively.  The  penetration  test  shall  also  be  made  on 
the  bituminous  material  under  the  following  conditions  when- 
ever practicable:  Penetration  at  4°  Cent.  (39°  Fahr.)  with  a 
weight  of  200  grams  for  i  minute;  penetration  at  46°  Cent. 
(115°  Fahr.)  with  a  weight  of  50  grams  for  5  seconds.  The 
loading  time  and  temperature  shall  be  reported  with  the  result- 
ing penetration  in  every  case.  The  unit  of  penetration  shall  be 
reported  as  o.i  mm. 

The  penetration  test  is  made  as  follows: 

The  sample  of  the  material  to  be  tested  shall  first  be  warmed 
just  sufficiently  to  flow  freely,  stirred  thoroughly,  and  poured  into 
a  flat-bottomed  tin  box,  5.715  cm.  (2.25  inches)  in  diameter,  and 
with  sides  about  3.810  cm.  (1.5  inches)  in  height.  The  box  and 
contents,  after  cooling  in  the  air  in  the  laboratory  for  10  minutes, 
shall  be  immersed  in  ice  water  for  20  minutes,  and  shall  then  be 
placed  in  water  maintained  at  the  temperature  at  which  the  ma- 
terial is  to  be  tested,  and  allowed  to  remain  immersed  for  2  hours, 
during  which  period  the  water  containing  the  sample  shall  be 
maintained  at  the  prescribed  temperature  accurately  and  con- 
stantly. The  sample,  in  a  glass  cup  and  covered  with  as  much 
water  at  the  temperature  at  which  the  material  is  to  be  tested 
as  may  be  convenient  without  spilling,  shall  now  be  removed  to 
the  penetrometer.  The  needle  shall  have  been  firmly  fixed  in 
the  machine  and  shall  now  be  lowered  with  its  holder  until  the 
point  of  the  needle  almost  touches  the  surface  of  the  sample. 


476  ELEMENTS   OF  HIGHWAY   ENGINEERING 

It  shall  then  be  cautiously  brought  down  until  the  point  of  the 
needle  just  comes  in  contact  with  the  surface  of  the  sample,  as 
will  best  be  seen  by  having  a  light  placed  in  such  a  way  that  on 
looking  through  the  sides  of  the  glass  cup  the  needle  will  be  re- 
flected from  the  surface  of  the  sample.  After  thus  setting  the 
needle,  the  rod  connected  with  the  recording  dial  shall  be  slowly 
lowered  until  the  foot  of  the  rod  shall  rest  on  the  head  of  that  part 
of  the  penetrometer  carrying  the  needle,  and  a  reading  of  the  dial 
shall  be  taken,  or  the  dial  shall  be  adjusted  to  read  at  a  convenient 
figure,  such  as  o  or  100. 

Simultaneously  noting  the  time  and  releasing  the  needle 
plunger,  which  shall  have  been  previously  weighted  properly 
for  the  particular  conditions  above  mentioned,  the  needle  shall 
be  allowed  to  act  freely  for  exactly  5  seconds,  as  determined  by  a 
pendulum  or  by  a  chronometer,  when  it  shall  be  stopped.  The 
rod  shall  then  be  lowered  until  it  rests  on  the  head  of  the  part  of 
the  instrument  carrying  the  needle,  and  the  difference  between 
the  first  and  second  readings  of  the  dial  shall  be  taken  as  the 
distance  penetrated  by  the  needle,  or  the  penetration. 

Owing  to  the  susceptibility  of  certain  bituminous  materials  to 
slight  changes  in  temperature,  the  water  bath  must  be  main- 
tained accurately  at  the  desired  temperature  both  before  and 
during  the  test,  and,  if  the  room  temperature  differs  greatly 
from  that  of  the  bath,  the  water  in  the  glass  cup  shall  be  renewed 
from  the  bath  after  each  trial.  An  average  of  from  three  to  five 
trials,  which  should  not  differ  from  one  another  more  than  three 
units,  shall  be  taken  as  the  penetration  of  the  sample. 

The  needle  shall  be  cleaned  thoroughly  by  wiping  with  a  dry 
cloth  before  and  after  each  trial.  The  point  of  the  needle  should 
be  examined  with  a  magnifying  glass  from  time  to  time  to  see  if 
it  has  become  injured  in  any  way.  If  it  is  found  to  be  defective, 
the  needle  shall  be  replaced  with  a  perfect  one.  Care  shall  be 
taken  that  the  needle,  in  place  in  the  machine  and  released  for 
action,  shall  be  loaded  as  required. 

MELTING  POINT 
The  material  under  examination  shall  be  first  melted  in  a 


APPENDIX   II  477 

spoon  by  the  gentle  application  of  heat  until  sufficiently  fluid  to 
pour  readily.  Care  shall  be  taken  that  it  suffers  Ao  appreciable 
loss  by  volatilization.  It  shall  then  be  poured  into  a  i2.7-mm. 
(o. 5-inch)  brass  cubical  mold,  which  shall  have  been  amalga- 
mated with  mercury  and  shall  be  placed  on  an  amalgamated  brass 
plate.  The  brass  may  be  amalgamated  by  washing  it  first  with  a 
dilute  solution  of  mercuric  chloride  or  nitrate,  after  which  the 
mercury  is  rubbed  into  the  surface.  By  this  means  the  bi- 
tuminous material  is,  to  a  considerable  extent,  prevented  from 
sticking  to  the  sides  of  the  mold.  The  hot  material  shall  slightly 
more  than  fill  the  mold,  and,  when  cooled,  the  excess  shall  be 
cut  off  with  a  hot  spatula. 

After  cooling  to  room  temperature,  the  cube  shall  be  removed 
from  the  mold  and  fastened  on  the  lower  arm  of  a  No.  10  wire 
(B.  &  S.  gauge),  bent  at  right  angles  at  one  end  and  suspended 
beside  a  thermometer  in  a  covered  Jena  glass  beaker  having  a 
capacity  of  400  cu.  cm.  (13.526  ounces),  which  shall  be  placed  in  a 
water  bath,  or,  for  high  temperatures,  a  cottonseed-oil  bath. 
The  wire  shall  be  passed  through  the  center  of  two  opposite  faces 
of  the  cube,  which  shall  then  be  suspended  with  its  base  25.4  mm. 
(i  inch)  above  the  bottom  of  the  beaker.  The  water  or  oil  bath 
shall  consist  of  an  8oo-cu.  cm.  (27.051  ounces)  low-form  Jena 
glass  beaker  suitably  mounted  for  the  application  of  heat  from 
below.  The  beaker  in  which  the  cube  is  suspended  shall  be  of  the 
tall-form  Jena  type,  without  lip.  The  metal  cover  shall  have 
two  openings.  A  cork,  through  which  passes  the  long  arm  of  the 
wire,  shall  be  inserted  in  one  hole  and  the  thermometer  in  the 
other.  The  bulb  of  the  thermometer  shall  be  just  level  with  the 
cube  and  at  an  equal  distance  from  the  side  of  the  beaker.  In 
order  that  a  reading  of  the  thermometer  may  be  made,  if  neces- 
sary, at  the  point  which  passes  through  the  cover,  the  hole  shall 
be  triangular  and  covered  with  an  ordinary  object  glass  through 
which  the  stem  of  the  thermometer  may  be  seen.  Readings  made 
through  this  glass  shall  be  calibrated  to  the  angle  of  observation, 
which  may  be  made  constant  by  sighting  always  from  the  front 
edge  of  the  opening  to  any  given  point  on  the  stem  of  the  ther- 
mometer below  the  cover. 


478  ELEMENTS   OF  HIGHWAY  ENGINEERING 

After  the  test  specimen  shall  have  been  placed  in  the  appara- 
tus, the  liquid  in  the  outer  vessel  shall  be  heated  in  such  a  manner 
that  the  thermometer  registers  an  increase  of  5°  Cent.  (9°  Fahr.) 
per  minute.  The  temperature  at  which  the  bituminous  material 
touches  a  piece  of  paper  placed  in  the  bottom  of  the  beaker  shall 
be  taken  as  the  melting  point.  Determinations  made  in  the  man- 
ner described  shall  not  vary  more  than  2°  Cent.  (3.6°  Fahr.)  for 
successive  trials  on  the  same  material.  At  the  beginning  of  this 
test  the  temperature  of  both  bituminous  material  and  bath  shall 
be  approximately  at  25°  Cent.  (77°  Fahr.). 


Loss  ON  EVAPORATION 

Fifty  grams  of  the  material  shall  be  heated  in  a  flat-bot- 
tomed dish,  5.715  cm.  (2.25  inches)  in  diameter  and  with  sides 
about  3.810  cm.  (1.5  inches)  high  for  a  total  of  5  hours  in  three 
successive  periods  of  3,  i,  and  i  hours,  respectively,  in  a  well- 
ventilated  oven,  the  interior  of  which  shall  be  maintained  at  a 
uniform  and  constant  temperature  of  163°  Cent.  (325°  Fahr.). 
The  oven  temperature  shall  be  controlled  by  any  thermo-regula- 
tor  effective  within  2°  Cent.  (3.6°  Fahr.),  and  shall  be  brought 
to  its  full  temperature  before  the  material  is  introduced.  The 
dish  shall  be  level,  and  its  contents,  without  removal  from  the 
oven,  shall  be  stirred  thoroughly  for  i  minute  between  the  suc- 
cessive periods  mentioned.  In  preparing  the  residue  for  the  pene- 
tration test,  it  shall  first  be  heated,  and  thoroughly  stirred  while 
cooling. 

DISTILLATION 

(Method  recommended  by  the  Sub-Committee  on  Distilla- 
tion of  the  American  Society  for  Testing  Materials.  Note: 
Equivalents  in  English  units  have  been  added  by  the  Special 
Committee  on  Materials  for  Road  Construction.) 

Sampling. — The  sample  as  received  shall  be  thoroughly 
stirred  and  agitated,  warming,  if  necessary,  to  insure  a  complete 
mixture  before  the  portion  for  analysis  is  removed. 

Dehydration. — If  the  presence  of  water  is  suspected,  or  known, 


APPENDIX   II  479 

the  material  shall  be  dehydrated  before  distillation.  About 
500  cu.  cm.  (16.907  ounces)  of  the  material  is  placed  in  an  8oo-cu. 
cm.  (27.051  ounces)  copper  still  provided  with  a  distilling  head 
connected  with  a  water-cooled  condenser.  A  ring  burner  is 
used,  starting  with  a  small  flame  at  the  top  of  the  still,  and  grad- 
ually lowering  it,  if  necessary,  until  all  the  water  has  been  driven 
off.  The  distillate  is  collected  in  a  200-01.  cm.  separatory  funnel 
with  the  tube  cut  off  close  to  the  stop-cock.  When  all  the  water 
has  been  driven  over  and  the  distillate  has  settled  out,  the  water 
is  drawn  off  and  the  oils  are  returned  to  the  residue  in  the  still. 
The  contents  of  the  still  shall  have  cooled  to  below  100°  Cent. 
(212°  Fahr.)  before  the  oils  are  returned,  and  they  shall  be  well 
stirred  and  mixed  with  the  residue. 

Apparatus. — The  apparatus  shall  consist  of  the  following 
standard  parts: 

(a)  Flask. — The   distillation   flask   shall   be   a   250-01.   cm. 
Engler  distilling  flask,  having  the  following  dimensions: 

Diameter  of  bulb 8.0  cm.  (3 . 1 50  in.) 

Length  of  neck 15.0  "  (5.906 

Diameter  of  neck 1.7  "  (o .  670 

Surface  of  material  to  lower  side  of  tubulature.   n  .o  "  (4.331 

Length  of  tubulature 15.0  "  (5 . 906 

Diameter  of  tubulature 0.9  "  (0.354 

Angle  of  tubulature 75° 

A  variation  of  3  percent  from  the  foregoing  measurements 
will  be  allowed. 

(b)  Thermometer. — The  thermometer  shall  be  of  hardened 
glass,  filled  with  carbon  dioxide  under  pressure,  and  provided  with 
an  expansion  chamber  at  the  top;  it  shall  read  to  450°  Cent. 
(842°  Fahr.),  shall  be  graduated  in  single  degrees,  centigrade,  and 
shall  have  the  following  dimensions: 

Diameter  of  stem 6. 75  to      7.25  mm.  (  0.266  to    0.286  in.) 

Length  of  thermometer 335         "  350                 (13.189  "  13.780  ") 

Length  from  o°  to  450°  marks ..  285         "300           "     (11.221  "  11.811    ") 

Length  of  bulb 20         "     22           "     (0.787"     0.866") 

Diameter  of  bulb 5.25  "       6.50     "     (  0.207  "     0.256  "  ) 

It  shall  rise  from  15°  to  95°  Cent.  (59°  to  203°  Fahr.)  in  not 
less  than  3  seconds  nor  more  than  5  seconds  when  plunged  into 
boiling  water. 


480  ELEMENTS   OF   HIGHWAY   ENGINEERING 

The  thermometer  shall  be  set  up  as  for  the  distillation  test, 
using  water,  naphthalene,  and  dime  thy  lamine  as  distilling  liquids. 
The  correctness  of  the  thermometer  shall  be  checked  at  o°  Cent. 
(32°  Fahr.)  and  100°  Cent.  (212°  Fahr.)  after  each  third  dis- 
tillation until  seasoned. 

(c)  Condenser. — The  condenser  tube  shall  have  the  following 
dimensions : 

Length .  .  .  500  mm.  (19 . 685  in.) 

Width 12  to    15  (0.472  to  0.591  in.) 

Width  of  adaptor  end 20  "     25     "     (0.787  "  0.984  "  ) 

(d)  Stands. — Two  iron  stands  shall  be  provided,  one  with  a 
universal  clamp  for  holding  the  condenser,  and  one  with  a  light 
grip  arm  with  a  cork-lined  clamp  for  holding  the  flask. 

(e)  Burner  and  Shield. — A  Bunsen  burner  shall  be  provided, 
with  a  tin  shield,  20  cm.  (7.784  inches)  long  and  9  cm.  (3.543 
inches)  in  diameter.     The  shield  shall  have  a  small  hole  through 
which  to  observe  the  flame. 

(/)  Cylinders. — The  cylinders  used  in  collecting  the  dis- 
tillate shall  have  a  capacity  of  25  cu.  cm.  (0.845  ounces),  and 
shall  be  graduated  in  tenths  of  a  cubic  centimeter. 

Setting  up  the  Apparatus. — The  apparatus  shall  be  set  up, 
the  thermometers  being  placed  so  that  the  top  of  the  bulb  is 
opposite  the  middle  of  the  tubulature.  All  connections  shall  be 
tight. 

Method. — One  hundred  cubic  centimeters  (3.381  ounces)  of 
the  dehydrated  material  to  be  tested  shall  be  placed  in  a  tared 
flask  and  weighed.  After  adjusting  the  thermometer,  shield, 
condenser,  etc.,  the  distillation  is  commenced,  the  rate  being 
regulated  so  that  i  cu.  cm.  (0.034  ounce)  passes  over  every 
minute.  The  receiver  is  changed  as  the  mercury  column  just 
passes  the  fractionating  point. 

Up  to  1 10°  Cent.  (230°  Fahr.) 

110°  Cent.  "    170°      "  (338°      "     ) 

i?o°  '    235°  (455°  ) 

235°  •'    270°  (518°  ) 

270°,     '         "    300°  (572°  ) 

To  determine  the  quantity  of  residue,  the  flask  is  weighed 
again  when  distillation  is  complete.  During  the  distillation  the 


APPENDIX   II  481 

condenser  tube  shall  be  warmed  when  necessary,  in  order  to  pre- 
vent the  deposition  of  any  sublimate.  The  percentages  of  frac- 
tion should  be  reported,  both  by  weight  and  by  volume. 

DUCTILITY 

A  briquette  of  the  material  to  be  tested  shall  be  formed  by 
pouring  the  molten  material  into  a  briquette  mold.  The  dimen- 
sions of  the  briquette  shall  be:  i  cm.  (0.394  inch)  in  thickness 
throughout  its  entire  length;  distance  between  the  clips  or  end 
pieces,  3  cm.  (1.181  inch);  width  of  asphalt  cement  Section  at 
mouth  of  clips,  2  cm.  (0.787  inch);  width  at  minimum  cross- 
section,  half  way  between  clips,  i  cm.  (0.394.  inch).  The  center 
pieces  are  removable,  the  briquette  mold  being  held  together 
during  molding  with  a  clamp  or  wire. 

The  molding  of  the  briquette  shall  be  done  as  follows:  The 
two  center  sections  shall  be  well  amalgamated  to  prevent  the 
asphalt  cement  from  adhering  to  them,  and  the  briquette  mold 
shall  then  be  placed  on  a  freshly  amalgamated  brass  plate.  The 
asphalt  cement  to  be  tested,  while  in  a  molten  state,  shall  be 
poured  into  the  mold,  a  slight  excess  being  added  to  allow  for 
shrinkage  on  cooling.  When  the  asphalt  cement  in  the  mold 
is  nearly  cool,  the  briquette  shall  be  cut  off  level,  with  a  warm 
knife  or  spatula.  When  it  is  thoroughly  cooled  to  the  tem- 
perature at  which  it  is  desired  to  make  the  test,  the  clamp  and 
the  two  side  pieces  are  removed,  leaving  the  briquette  of  asphalt 
cement  held  at  each  end  by  the  ends  of  the  mold,  which  now  play 
the  part  of  clips.  The  briquette  shall  be  kept  in  water  for  30 
minutes  at  4°  Cent.  (39°  Fahr.)  or  25°  Cent.  (77°  Fahr.)  before 
testing,  dependent  on  the  temperature  at  which  the  ductility  is 
desired.  The  briquette  with  the  clips  attached  shall  then  be 
placed  in  a  " ductility  test  machine"  filled  with  water  at  one  of 
the  above  temperatures  to  a  sufficient  height  to  cover  the  bri- 
quette not  less  than  50  mm.  (1.969  inch).  This  machine  consists 
of  a  rectangular  water-tight  box,  having  a  movable  block  work- 
ing on  a  worm-gear  from  left  to  right.  The  left  clip  is  held  rigid 
by  placing  its  ring  over  a  short  metal  peg  provided  for  this  pur- 


482  ELEMENTS    OF   HIGHWAY   ENGINEERING 

pose;  the  right  clip  is  placed  over  a  similar  rigid  peg  on  the  mov- 
able block.  The  movable  block  is  provided  with  a  pointer  which 
moves  along  a  centimeter  scale.  Before  starting  the  test,  the 
centimeter  scale  is  adjusted  to  the  pointer  at  zero.  Power  is 
then  applied  by  the  worm-gear  pulling  from  left  to  right  at  the 
uniform  rate  of  5  cm.  (1.969  inches)  per  minute.  The  distance,  in 
centimeters,  registered  by  the  pointer  on  the  scale  at  the  time 
of  rupture  of  the  thread  of  asphalt  cement  shall  be  taken  as  the 
ductility  of  the  asphalt  cement. 

SOLUBILITY  IN  PETROLEUM  NAPHTHA,  AND   CHARACTER 
OF  RESIDUE  ON  GLASS 

Two  grams  of  the  material  shall  be  placed  in  a  4-ounce  oil- 
sample  bottle,  made  up  to  100  cu.  cm.  (3.381  ounces)  with  88° 
Baume  petroleum  naphtha  (boiling  point  between  40°  Cent. 
(104°  Fahr.)  and  55°  Cent.  (131°  Fahr.),  and  the  whole  well 
shaken  until  the  sample  is  digested.  The  bottle  shall  then  be 
centrifugalized  for  10  minutes,  50  cu.  cm.  (1.691  ounces)  with- 
drawn into  a  weighed  flask,  the  naphtha  distilled  off  by  a  water 
bath,  and  the  residue  weighed.  From  this  weight  the  percentage 
of  solubility  shall  be  calculated. 

Although  there  is  no  generally  accepted  method  of  determin- 
ing the  stickiness  or  oiliness  of  bituminous  materials,  except  by 
the  unsatisfactory  method  of  handling,  a  test  which  has  been  used 
to  a  limited  extent,  and  is  based  on  the  character  of  the  residue 
on  glass,  appears  to  the  Committee  to  give  promise.  This  test 
is  made  as  follows: 

One-half  gram  of  the  residue  obtained  as  just  specified  shall 
then  be  placed  in  the  center  of  a  circular  glass  disk,  32.258  sq. 
cm.  (5  sq.  inches)  in  area,  and  a  similar  disk  shall  be  imposed  upon 
it.  By  warming  and  pressure  of  the  ringers  the  material  shall  be 
as  evenly  distributed  as  practicable  over  the  adjacent  surfaces, 
of  the  disks,  and  the  disks  with  the  material  between  them  shall 
then  be  stored  under  a  weight  of  i  kg.  and  at  a  temperature  of 
25°  Cent.  (77°  Fahr.)  for  at  least  2  hours.  The  disks  shall  then 
be  pulled  apart  horizontally  and  in  a  direction  truly  parallel  to. 


APPENDIX   II  483 

their  facial  diameters  at  a  regular  rate  of  movement  of  2.540  cm. 
(i  inch)  per  minute,  the  maximum  stress,  in  grams,  required 
being  recorded  and  reported. 

FIXED  CARBON 

One  gram  of  the  bituminous  material  shall  be  placed  in  a 
platinum  crucible  weighing  between  20  and  30  grams,  between 
28  and  38  mm.  (1.102  and  1.496  inches)  in  height,  and  having  a 
tightly  fitting  cover  provided  with  a  flange  about  4  mm.  (0.157 
inch)  in  depth.  The  crucible  and  its  contents  shall  then  be 
heated,  first  gently  and  then  more  severely,  until  no  smoke  or 
flame  shall  issue  between  the  crucible  and  the  lid.  It  shall  then 
be  placed  in  the  full  flame  of  a  Bunsen  burner  for  7  minutes,  hold- 
ing the  cover  down  with  the  end  of  a  pair  of  tongs  until  the  most 
volatile  products  shall  have  been  burned  off.  The  crucible  shall 
be  supported  on  a  platinum  triangle  with  the  bottom  6  to  8  cm. 
(2.362  to  3.150  inches)  above  the  top  of  the  burner.  The  flame 
shall  be  fully  20  cm.  (7.874  inches)  high  when  burning  free,  and 
the  determination  shall  be  made  in  a  place  free  from  drafts.  The 
upper  surface  of  the  cover  shall  burn  clear,  but  the  under  surface 
may  or  may  not  be  covered  with  carbon,  dependent  on  the  charac- 
ter of  tjie  bituminous  material.  The  crucible  shall  be  removed 
to  the  desiccator,  and,  when  cool,  shall  be  weighed,  after  which 
the  cover  shall  be  removed  and  the  crucible  placed  in  an  inclined 
position  over  the  Bunsen  burner  and  ignited  until  nothing  but 
ash  remains.  Any  carbon  deposited  on  the  cover  shall  also  be 
burned  off.  The  weight  of  ash  remaining  shall  be  deducted 
from  the  weight  of  the  residue  after  the  first  ignition  of  the  sample. 
The  resulting  weight  is  that  of  the  fixed  carbon,  which  shall  be 
calculated  on  the  basis  of  the  total  weight  of  the  sample,  ex- 
clusive of  mineral  matter. 

PARAFFIN 

One  hundred  grams  of  the  material  shall  be  distilled  rapidly 
in  a  retort  to  a  dry  coke.  Five  grams  of  the  distillate  shall 


484  ELEMENTS    OF   HIGHWAY   ENGINEERING 

then  be  thoroughly  mixed  in  a  60  cu.  cm.  (2.029  ounce)  flask 
with  25  cu.  cm.  (0.845  ounce)  of  Squibbs-  absolute  ether.  Twenty- 
five  cu.  cm.  (0.845  ounce)  of  Squibbs'  absolute  alcohol  shall  then 
be  added,  and  the  flask  packed  closely  in  a  freezing  mixture  of 
finely  crushed  ice  and  salt  for  at  least  30  minutes.  The  pre- 
cipitate shall  be  filtered  out  quickly  with  a  suction  pump,  using 
a  No.  575  C.  S.  and  S.  9  cm.  hardened  filter  paper.  The  flask 
and  precipitate  shall  then  be  rinsed  and  washed  with  a  mixture 
of  equal  parts  of  Squibbs'  alcohol  and  ether  cooled  to  — 17°  Cent. 
(i°Fahr.)  until  free  from  oil  (50  cu.  cm.  (1.691  ounces)  of  washing 
solution  is  usually  sufficient) .  When  sucked  dry,  the  filter  paper 
shall  be  removed  and  the  waxy  precipitate  transferred  to  a  small 
glass  disk  and  evaporated  on  a  steam  bath.  The  residue  (paraffin) 
remaining  on  the  disk  shall  be  weighed,  and  from  this  weight  the 
percentage  on  the  original  5-gram  sample  shall  be  calculated. 

(Note:  Although  the  foregoing  method  is  the  one  in  general 
use,  the  following  modification  is  believed  by  the  Committee  to 
promise  accurate  results  and  to  merit  thorough  trial.) 

One  hundred  grams  of  the  material  shall  be  distilled  rapidly 
in  a  retort  to  dry  coke.  The  distillate  shall  then  be  thoroughly 
mixed.  A  5-gram  sample  of  the  distillate  shall  be  placed  in  a 
tared  60  cu.  cm.  (2.029  ounce)  flask  with  25  cu.  cm.  (0.845 
ounce)  of  Squibbs'  ether.  Twenty-five  cubic  centimeters  (0.845 
ounce)  of  Squibbs'  alcohol  shall  be  added,  after  which  the 
mixture  shall  be  shaken  well  and  the  flask  packed  closely  in  a 
freezing  mixture  of  finely  crushed  ice  and  salt  for  at  least  30 
minutes.  Without  removing  the  flask  from  the  freezing  mixture, 
the  solvent  shall  be  sucked  from  the  precipitated  paraffin  by 
using  a  tube  connected  with  the  filter  pump,  the  end  of  the  tube 
being  covered  with  an  accurately  weighed  tuft  of  absorbent 
cotton.  When  the  solvent  is  all  removed,  the  flask  shall  be 
taken  from  the  freezing  mixture  and  the  cotton  tuft  pushed  off 
the  tube  into  the  flask.  The  waxy  precipitate  shall  be  dissolved, 
with  the  tuft  of  cotton,  in  25  cu.  cm.  (0.845  ounce)  of  Squibbs' 
absolute  ether.  Twenty-five  cubic  centimeters  (0.845  ounce)  of 
Squibbs'  absolute  alcohol  shall  then  be  added  and  the  flask 
placed  in  the  freezing  mixture  again  for  30  minutes.  The 


APPENDIX   II  485 

solvent  shall  then  be  removed  with  the  pump  and, tube  as  de- 
scribed previously,  keeping  the  flask  in  the  freezing  mixture. 
The  second  cotton  tuft  shall  be  pushed  into  the  flask.  The  flask 
and  contents  shall  then  be  placed  in  the  drying  oven  at  100° 
Cent.  (212°  Fahr.)  until  constant  weight  shall  be  reached.  This 
weight,  less  the  weight  of  the  cotton  used  and  less  the  weight 
of  the  tared  flask,  is  the  weight  of  the  paraffin.  Calculate  the 
weight  of  the  paraffin  to  a  percentage  of  the  original  material. 


APPENDIX  III 
TESTS  OF  NON-BITUMINOUS  HIGHWAY  MATERIALS 

Methods  for  performing  tests  to  determine  the  physical  prop- 
erties of  non-bituminous  highway  materials  which  have  been 
adopted  by  the  American  Society  for  Testing  Materials  are 
designated  thus,  *;  those  proposed  by  the  Committee  on  "Stand- 
ard Tests  for  Road  Materials"  (Committee  D-4)  of  the  American 
Society  for  Testing  Materials  have  been  noted  thus,  f>  those 
proposed  by  the  Committee  on  "Standard  Specifications  for 
Brick"  (Committee  0-3)  of  the  American  Society  for  Testing 
Materials  have  been  indicated  thus,  {;  and  those  recommended 
by  the  United  States  Office  of  Public  Roads  and  Rural  Engi- 
neering have  been  indicated  thus,  ft- 

APPARENT  SPECIFIC  GRAVITY  OF  ROCKJ 

"The  apparent  specific  gravity  of  rock  shall  be  determined 
by  the  following  method:  First,  a  sample  weighing  between  29 
and  31  grams,  approximately  cubical  in  shape,  shall  be  dried  in 
a  closed  oven  for  i  hour  at  a  temperature  of  110°  C.  (230°  F.) 
and  then  cooled  in  a  desiccator  for  i  hour;  second,  the  sample 
shall  be  rapidly  weighed  in  air;  third,  trial  weighings  in  air 
and  in  water  of  another  sample  of  approximately  the  same  size 
shall  be  made  in  order  to  determine  the  approximate  loss  in 
weight  on  immersion;  fourth,  after  the  balances  shall  have  been 
set  at  the  calculated  weight,  the  first  sample  shall  be  weighed 
as  quickly  as  practicable  in  distilled  water  having  a  temperature 
of  25°  C.  (77°  F.);  fifth,  the  apparent  specific  gravity  of  the 
sample  shall  be  calculated  by  the  following  formula: 

W 
Apparent  specific  gravity  =        _ 

in  which  W  =  the  weight  in  grams  of   the   sample  in  air  and 
Wi  =  the  weight  in  grams  of    the  sample  in  water   just  after 

486 


APPENDIX   III  487 

immersion.  Finally,  the  apparent  specific  gravity  of  the  rock 
shall  be  the  average  of  three  determinations,  made  on  three 
different  samples  according  to  the  method  above  described." 

APPARENT  SPECIFIC  GRAVITY  or  SAND,  STONE  SCREENINGS,  OR 
OTHER  FINE  HIGHWAY  MATERIAL 

APPARATUS.  The  determination  shall  be  made  with  a  Jackson 
specific  gravity  apparatus,  which  shall  consist  of  a  burette, 
with  graduations  reading  to  o.oi  in  specific  gravity,  about  23  cm. 
(9  inches)  long  and  with  an  inside  diameter  of  about  0.6  cm. 
(0.25  inch),  which  shall  be  connected  with  a  glass  bulb  approxi- 
mately 13  cm.  (5.5  inches)  long  and  4.5  cm.  (1.75  inches)  in 
diameter,  the  glass  bulb  being  of  such  size  that  from  a  mark 
on  the  neck  at  the  top  to  a  mark  on  the  burette  just  below  the 
bulb  the  capacity  is  exactly  180  cu.  cm.;  and  an  Erlenmeyer 
flask  which  shall  contain  a  hollow  ground  glass  stopper  having 
the  neck  of  the  same  bore  as  the  burette  and  a  capacity  of 
exactly  200  cu.  cm.  up  to  the  graduation  on  the  neck  of  the 
stopper. 

METHOD  OF  DETERMINATION.  The  method  shall  consist  of, 
first,  drying  at  not  over  110°  C.  (230°  F.)  to  a  constant  weight 
a  sample  weighing  about  55  grams;  second,  weigh  out  accu- 
rately to  o.i  gram,  50  grams  of  the  dry  sample  and  pour  it 
into  the  unstoppered  Erlenmeyer  flask;  third,  fill  the  bulb  and 
burette  with  kerosene,  leaving  just  space  enough  to  take  the 
temperature  by  introducing  a  thermometer  through  the  neck; 
fourth,  remove  the  thermometer  and  add  sufficient  kerosene  to 
fill  exactly  to  the  mark  on  the  neck,  drawing  off  any  excess  by 
means  of  the  burette;  fifth,  run  into  the  flask  about  one-half 
of  the  kerosene  in  the  bulb  to  remove  air  bubbles  and  then 
run  in  more  kerosene,  removing  any  material  adhering  to  the 
neck  of  the  flask  until  the  kerosene  is  just  below  the  ground 
glass;  sixth,  place  the  hollow  ground  glass  stopper  in  position 
and  turn  it  to  fit  tightly  and  then  run  in  kerosene  exactly  to 
the  200  cu.  cm.  graduation  on  the  neck,  care  being  taken  to 
remove  all  air  bubbles  in  the  flask;  seventh,  read  the  specific 


488  ELEMENTS    OF   HIGHWAY   ENGINEERING 

gravity  from  the  graduation  on  the  burette  and  the  tempera- 
ture of  the  oil  in  the  flask,  noting  the  difference  between  the 
temperature  of  the  oil  in  the  bulb  before  the  determination 
and  the  temperature  of  the  oil  in  the  flask  after  the  determina- 
tion; eighth,  make  a  temperature  correction  to  the  reading  of 
the  specific  gravity  in  accordance  with  the  table  furnished  by 
the  manufacturer  of  the  apparatus,  adding  the  correction  if 
the  temperature  of  the  kerosene  has  increased  and  subtracting 
the  correction  if  the  temperature  of  the  kerosene  has  decreased. 

ABSORPTION   OF  WATER  PER   CUBIC   FOOT  OF   Rocxf 

"The  absorption  of  water  per  cubic  foot  of  rock  shall  be 
determined  by  the  following  method:  First,  a  sample  weighing 
between  29  and  31  grams,  and  approximately  cubical  in  shape, 
shall  be  dried  in  a  closed  oven  for  i  hour  at  a  temperature  of 
110°  C.  (230°  F.)  and  then  cooled  in  a  desiccator  for  i  hour; 
second,  the  sample  shall  be  rapidly  weighed  in  air;  third,  trial 
weighings  in  air  and  in  water  of  another  sample  of  approximately 
the  same  size  shall  be  made  in  order  to  determine  the  approxi- 
mate loss  in  weight  on  immersion;  fourth,  after  the  balances 
shall  have  been  set  at  the  calculated  weight,  the  first  sample 
shall  be  weighed  as  quickly  as  possible  in  distilled  water  having 
a  temperature  of  25°  C.  (77°  F.);  fifth,  allow  the  sample  to 
remain  48  hours  in  distilled  water  maintained  as  nearly  as  prac- 
ticable at  25°  C.  (77°  F.)  at  the  termination  of  which  time 
bring  the  water  to  exactly  this  temperature  and  weigh  the  sample 
while  immersed  in  it;  sixth,  the  number  of  pounds  of  water 
absorbed  per  cubic  foot  of  the  sample  shall  be  calculated  by 
the  following  formula: 


*  —      i 

Pounds  of  water  absorbed  per  cubic  foot  =  -==  -  —  X  62.24 

W  —  W\ 

in  which  W  =  the  weight  in  grams  of  sample  in  air,  W\  =  the 
weight  in  grams  of  sample  in  water  just  after  immersion,  W%  = 
the  weight  in  grams  of  sample  in  water  after  48  hours  immer- 
sion, and  62.24  =  the  weight  in  pounds  of  a  cubic  foot  of  dis- 


APPENDIX   III  489 

tilled  water  having  a  temperature  of  25°  C.  (77°  F.).  Finally, 
the  absorption  of  water  per  cubic  foot  of  the  rock,  in  pounds, 
shall  be  the  average  of  three  determinations  made  on  three 
different  samples  according  to  the  method  above  described." 

ABRASION  TEST  FOR  ROCK  OR  SLAG* 

"The  machine  shall  consist  of  one  or  more  hollow  iron  cylin- 
ders closed  at  one  end  and  furnished  with  a  tightly  fitting 
iron  cover  at  the  other;  the  cylinders  to  be  20  cm.  in  diameter 
and  34  cm.  in  depth,  inside.  These  cylinders  are  to  be  mounted 
on  a  shaft  at  an  angle  of  30  degrees  with  the  axis  of  rotation 
of  the  shaft,  see  Fig.  60. 

"At  least  30  pounds  of  coarsely  broken  stone  shall  be  avail- 
able for  a  test.  The  rock  to  be  tested  shall  be  broken  in  pieces 
as  nearly  uniform  in  size  as  possible,  and  as  nearly  50  pieces 
as  possible  shall  constitute  a  test  sample.  The  total  weight  of 
rock  in  a  test  shall  be  within  10  grams  of  5  kilograms.  All  test 
pieces  shall  be  washed  and  thoroughly  dried  before  weighing. 
Ten  thousand  revolutions,  at  the  rate  of  between  30  and  33  to 
the  minute,  shall  constitute  a  test.  Only  the  percentage  of 
material  worn  off  which  will  pass  through  a  0.16  cm.  (/{$  inch) 
mesh  sieve  shall  be  considered  in  determining  the  amount  of 
wear.  This  may  be  expressed  either  as  the  percentage  of  the 
5  kilograms  used  in  the  test,  or  the  French  coefficient,  which 
is  in  more  general  use,  may  be  given,  that  is,  coefficient  of 

20      400 
wear  =20  X  — =  — ,  where  w  is  the  weight  in  grams  of  the 

w        w 

detritus  under  0.16  cm.  (/{$  inch)  in  size  per  kilogram  of  rock 
used." 

ABRASION  TEST  FOR  GRAVEL 

The  test  for  abrasion  of  gravel  shall  be  made  with  a  Deval 
abrasion  machine,  see  Fig.  60,  which  shall  meet  the  following 
specifications:  the  machine  shall  consist  of  one  or  more  hollow 
iron  cylinders,  the  inside  dimensions  of  each  of  which  shall  be 
20  cm.  (7.87  inches)  in  diameter  and  34  cm.  (13.39  inches)  in 


490  ELEMENTS   OF   HIGHWAY   ENGINEERING 

depth;  the  cylinders  shall  be  closed  at  one  end  and  furnished 
with  a  tightly  fitting  iron  cover  at  the  other  end,  and  be  mounted 
on  a  shaft  at  an  angle  of  30  degrees  with  the  axis  of  rotation 
of  the  shaft. 

A  charge  of  gravel  shall  consist  of  pieces  which  shall  pass  a 
screen  having  circular  openings  5.08  cm.  (2  inches)  in  diameter 
and  be  retained  on  a  screen  having  circular  openings  1.27  cm. 
(0.5  inches)  in  diameter.  The  total  weight  of  gravel  in  a  charge 
shall  be  within  10  grams  of  5  kilograms.  The  gravel  to  com- 
pose a  charge  shall  be  washed,  and  dried  in  a  closed  oven  for 
i  hour  at  a  temperature  within  5  degrees  of  110°  C.  (230°  F.). 
The  charge  of  gravel  shall  be  placed  in  one  cylinder  of  the 
machine,  which  shall  be  rotated  at  a  rate  of  not  less  than  30 
nor  more  than  33  revolutions  per  minute.  Ten  thousand  revo- 
lutions shall  constitute  a  test.  The  percentage  of  material  worn 
off  which  will  pass  through  a  sieve,  having  openings  of  0.16  cm. 
(%6  inch),  shall  be  considered  the  amount  of  wear  of  the 
charge  of  gravel.  The  loss  by  abrasion,  determined  as  stated, 
shall  be  expressed  in  terms  of  the  percentage  of  the  total  weight 
of  the  charge  of  gravel. 

TOUGHNESS  TEST  FOR  ROCK,  SLAG,  OR  SIMILAR  MATERIAL* 

"i.  Test  pieces  may  be  either  cylinders  or  cubes,  25  mm. 
in  diameter,  and  25  mm.  in  height,  cut  perpendicular  to  the 
.cleavage  of  the  rock.  Cylinders  are  recommended  as  they  are 
cheaper  and  more  easily  made. 

"2.  The  testing  machine,  see  Fig.  62,  shall  consist  of  an 
anvil  of  50  kilograms  weight,  and  placed  on  a  concrete  founda- 
tion. The  hammer  shall  be  of  2  kilograms  weight,  and  dropped 
upon  an  intervening  plunger  of  i  kilogram  weight,  which  rests 
on  the  test  piece.  The  lower  or  bearing  surface  of  this  plunger 
shall  be  of  spherical  shape  having  a  radius  of  i  cm.  This  plunger 
shall  be  made  of  hardened  steel,  and  pressed  firmly  upon  the 
test  piece  by  suitable  springs.  The  test  piece  shall  be  adjusted, 
so  that  the  center  of  its  upper  surface  is  tangent  to  the  spherical 
end  of  the  plunger. 


APPENDIX   III  491 

"3.  The  test  shall  consist  of  a  i  cm.  fall  of  the  hammer  for 
the  first  blow,  and  an  increased  fall  of  i  cm.  for  each  succeeding 
blow  until  failure  of  the  test  piece  occurs.  The  number  of 
blows  necessary  to  destroy  the  test  piece  is  used  to  represent 
the  toughness,  or  the  centimeter-grams  of  energy  applied  may 
be  used." 

HARDNESS  TEST  FOR  ROCK  OR  SLAG  ft 

"The  test  for  the  hardness  of  rock,  i.  e.,  the  resistance  of  its 
surface  particles  to  displacement  by  abrasion,  as  determined  in 
the  Dorry  machine,  was  developed  in  the  French  School  of 
Bridges  and  Roads  and  is  used  with  slight  modifications  at  the 
present  day. 

"The  Dorry  machine,  see  Fig.  63,  consists  of  a  circular  steel 
disk,  revolving  in  a  horizontal  plane  about  a  vertical  shaft, 
which  is  driven  from  the  pulley  by  means  of  a  bevel  gear.  The 
cylindrical  rock  core,  25  mm.  in  diameter,  is  cut  from  a  specimen 
of  rock  with  a  diamond  core  drill,  and  the  test  piece  is  held 
perpendicularly  against  a  revolving  cast-steel  disk  under  a  con- 
stant pressure  of  1,250  grams,  while  standard  quartz  sand,  be- 
tween 30  and  40  mesh,  is  fed  on  the  disk  to  act  as  the  abrasive 
agent.  The  machine  used  is  arranged  to  hold  two  core  pieces 
so  that  two  tests  can  be  run  simultaneously.  At  the  end  of 
1,000  revolutions  the  loss  in  weight  is  determined  and  the  test 
repeated  with  the  specimen  reversed.  The  average  loss  in  weight 
computed  from  the  two  runs  is  used  in  determining  the  hard- 
ness of  the  rock.  In  the  earlier  work  the  loss  in  length  was 
determined  from  measurements  taken  before  and  after  each  run, 
and  the  average  loss  expressed  in  millimeters  per  1,000  revolu- 
tions subtracted  from  20  was  given  as  representing  the  hardness 
of  the  specimen.  The  arbitrary  constant  20  was  selected  with 
a  view  to  giving  the  results  of  this  test  about  the  same  range 
of  variation  as  the  French  coefficient  of  wear  described  under 
the  abrasion  test.  It  has  been  found,  however,  that  the  hard- 
est rocks  lose  only  about  2  mm.  per  1,000  revolutions,  while 
some  of  the  softer  varieties  lose  considerably  more  than  20  mm., 


492  ELEMENTS   OF   HIGHWAY   ENGINEERING 

thus  giving  rise  to  negative  values  in  the  results  of  the  test.  In 
order  to  avoid  this,  the  following  method  of  expressing  the 
hardness  has  been  adopted: 

Hardness,  H  =  20  —  yz  W, 
where  W  =  loss  in  grams  per  1,000  revolutions." 

CEMENTATION  TEST  FOR  ROCK  POWDERS  ft 

"The  following  method  for  testing  the  cementing  value  of 
rock  powders  was  devised  and  perfected  by  Mr.  Logan  Waller 
Page.  One-half  kilogram  of  the  rock  to  be  tested  is  broken 
sufficiently  small  to  pass  a  ^-inch  mesh  screen.  This  material 
is  placed  in  a  ball  mill  with  about  90  cu.  cm.  of  water,  sufficient 
to  make  a  stiff  paste  after  grinding.  The  material  is  ground 
by  the  action  of  tow  cast-steel  shot,  2^2  inches  in  diameter  and 
weighing  about  20  pounds.  Grinding  is  continued  for  2^2  hours 
at  the  rate  of  2,000  revolutions  per  hour,  after  which  the  'dough' 
is  removed  and  molded  into  cylindrical  briquettes  25  mm.  in 
diameter  and  25  mm.  high,  in  a  special  briquette-forming  ma- 
chine. Five  briquettes  are  made  from  each  test  sample  and 
allowed  to  dry  20  hours  in  air  and  4  hours  in  a  hot-air  bath  at 
200°  F.  After  cooling  20  minutes  in  a  desiccator,  they  are 
tested  by  impact  in  a  machine  especially  designed  for  the  pur- 
pose, see  Fig.  61.  A  motor  drives  a  cam  at  the  rate  of  60  revo- 
lutions per  minute,  by  means  of  a  worm  gear.  The  rise  of  the 
cam  is  such  as  to  give  an  effective  drop  of  one  centimeter  to 
the  hammer.  The  reaction  of  the  briquette  after  each  blow  of 
the  hammer  produces  a  vertical  movement  in  the  end  of  a  lever. 
This  motion  is  recorded  on  a  sheet  of  silicated  paper  wrapped 
around  the  recording  drum  by  means  of  a  brass  point  at  the 
end  of  the  lever.  Each  revolution  of  the  cam  produces  a  slight 
motion  of  the  drum,  so  that  the  drum  makes  a  complete  revo- 
lution in  100  revolutions  of  the  cam.  The  number  of  blows 
necessary  to  destroy  the  resilience  of  the  briquette,  so  that  no 
reaction  is  recorded  on  the  drum,  is  taken  to  be  the  cementing 
value  of  the  material." 


APPENDIX   III  493 

MECHANICAL  ANALYSIS  OF  BROKEN  STONE,  BROKEN  SLAG, 

OR  GRAVEL 

The  method  shall  consist  of,  first,  drying  at  not  over  110°  C. 
(230°  F.)  to  a  constant  weight  a  sample  weighing  in  pounds 
six  times  the  diameter  in  inches  of  the  largest  holes  required; 
second,  passing  the  sample  through  such  of  the  following  sized 
screens  having  circular  openings  as  are  required  or  called  for 
by  the  specifications,  screens  to  be  used  in  the  order  named: 
8.89  cm.  ($y2  inches),  7.62  cm.  (3  inches),  6.35  cm.  (2% 
inches),  5.08  cm.  (2  inches),  3.81  cm.  (1^2  inches),  3.18  cm. 
(1^4  inches),  2.54  cm.  (i  inch),  1.90  cm.  (^  inch),  1.27  cm. 
(>2  inch),  and  0.64  cm.  (^  inch);  third,  determining  the  per- 
centage by  weight  retained  on  each  screen;  fourth,  recording 
the  mechanical  analysis  in  the  following  manner : 

Percentage  passing  o.64-cm.  (>£-in.)  screen  = 
i.27-cm.  (K-in.) 
i  .go-cm.  (K^-in.)  = 

2.54-cm.  (  i -in.)       "       = 


100.00 

MECHANICAL  ANALYSIS  OF  SAND  OR  OTHER  FINE 
HIGHWAY  MATERIAL 

The  method  shall  consist  of,  first,  drying  at  not  over  110°  C. 
(230°  F.)  to  a  constant  weight  a  sample  weighing  100  grams; 
second,  passing  the  sample  through  each  of  the  following  mesh 
sieves  (American  Society  for  Testing  Materials  standard  sieves), 
the  sieves  to  be  used  in  the  order  named: 

Meshes  per  linear  Diameter  of  Wire 
Inch  (2. 54  cm.)  Ins.  Mm. 

10 0.027  0.6858 

20 0.0165  0.4191 

30 0.1375  0.34925 

40 0.01025  0.26035 

50 0.009  0.22865 

80 0.00575  0.1460 

100 0.0045  0.1143 

200 0 . 00235  O . 05969 

third,  determining  the  percentage  by  weight  retained  on  each 
sieve,  the  sifting  being  continued  on  each  sieve  until  less  than 


494  ELEMENTS    OF   HIGHWAY   ENGINEERING 

i  percent  of  the  weight  retained  on  each  sieve  shall  pass 
through  the  sieve  during  the  last  minute  of  sifting;  fourth, 
recording  the  mechanical  analysis  in  the  following  manner: 

Percentage  passing  2oo-mesh  sieve  = 

100      "         "  = 
80 

50      "         "  = 


IOO.OO 


MECHANICAL  ANALYSIS  OF  MIXTURES  OF  SAND  OR  OTHER  FINE 
HIGHWAY  MATERIAL  WITH  BROKEN  STONE,  BROKEN  SLAG, 

OR  GRAVEL 

The  method  shall  consist  of,  first,  drying  at  not  over  110°  C. 
(230°  F.)  to  a  constant  weight  a  sample  weighing  in  pounds 
six  times  the  diameter  in  inches  of  the  largest  holes  required; 
second,  separating  the  sample  by  the  use  of  a  lo-mesh  sieve 
(American  Society  for  Testing  Materials  standard  sieve);  third, 
examining  the  portion  retained  on  the  lo-mesh  sieve  in  accor- 
dance with  the  method  for  making  a  "Mechanical  Analysis  of 
Broken  Stone,  Broken  Slag,  or  Gravel";  fourth,  examining  the 
portion  passing  the  lo-mesh  sieve  in  accordance  with  the  method 
for  making  a  "Mechanical  Analysis  of  Sand  or  Other  Fine  High- 
way Material";  fifth,  recording  the  mechanical  analysis  in  the 
following  manner: 

Percentage  passing  2OO-mesh  sieve 

"  "        100     '  = 

80     " 


Percentage  passing  lo-mesh  sieve  = 

o.64-cm.  (>4-in.)  screen  = 
i.27-cm.  (j^-in.)  "  = 
1.90-cm.  (K-in.)  "  = 


IOO.OO 


VOIDS  IN  MINERAL  AcGREGATEsf 

"  The  voids  in  mineral  aggregates  shall  be  determined  by  the 
Cone  Specific  Gravity  method.     In  the  method  of  making  the 


APPENDIX   III  495 

determination  of  voids,  as  hereinafter  described,  there  shall  be 
used  a  truncated  cone  made  of  No.  18  B.  &  S. -gauge  galvanized 
steel  with  calked  seams  and  having  the  following  dimensions: 
overall  diameter  of  bottom,  25.4  cm.  (10  inches);  overall  height, 
25.4  cm.  (10  inches);  inside  diameter  of  opening,  7.6  cm.  (3 
inches) .  The  test  shall  be  made  in  the  following  manner :  First, 
thoroughly  mix  the  aggregate  by  rolling  on  paper;  second,  fill 
the  cone  with  aggregate,  avoiding  segregation;  third,  compact 
aggregate  in  cone  by  oscillation  on  edge  of  cone  resting  on 
wooden  floor,  wooden  box,  or  block  of  wood  and  use  cotton  waste 
pressed  against  surface  of  aggregate  to  prevent  segregation 
during  oscillation;  fourth,  continue  to  add  aggregate  and  com- 
pact until  the  cone  is  full  of  thoroughly  compacted  aggregate, 
which  process  will  require  from  300  to  500  oscillations;  fifth, 
weigh  cone  with  aggregate;  sixth,  weigh  cone  empty;  seventh, 
weigh  cone  full  of  clean  water;  eighth,  determine  the  specific 
gravity  of  aggregate;  ninth,  the  percentage  of  voids  in  the 
aggregate  shall  be  calculated  by  the  following  formula: 

/          (C  —  A)  \ 
Percentage  of  Voids  =  ( i  —  — — jryj    I0° 

*  \Jj        A )  L)' 

in  which  A  =  the  weight  in  grams  of  the  cone;  B  =  the  weight 
in  grams  of  the  cone  filled  with  water ;  C  =  the  weight  in  grams 
of  the  cone  filled  with  compacted  aggregate;  D  =  the  specific 
gravity  of  the  aggregate." 

RATTLER  TEST  FOR  PAVING  BRICK  { 

"CONSTRUCTION  OF  THE  RATTLER.     General  Design.     The 

machine  shall  be  of  good  mechanical  construction,  self-con- 
tained, and  shall  conform  to  the  following  details  of  material 
and  dimensions,  and  shall  consist  of  barrel,  frame,  and  driving 
mechanism  as  herein  described.  (Note  by  Author.  "The 

I  Abstracts  from  "Proposed  Standard  Specifications  for  Paving  Brick" 
recommended  for  adoption  at  the  1915  Annual  Meeting  of  the  American 
Society  for  Testing  Materials  by  Committee  C-3  on  "-Standard  Specifications 
for  Brick." 


496  ELEMENTS    OF   HIGHWAY  ENGINEERING 

Standard  Rattler  for  Testing  Paving  Brick"  proposed  by  The 
National  Paving  Brick  Manufacturers'  Association  on  Decem- 
ber i,  1910,  meets  the  requirements  of  the  specifications  of 
Committee  €-3.) 

"The  Barrel.  The  barrel  of  the  machine  shall  be  made  up 
of  the  heads,  headliners,  staves,  and  stave-liners." 

"The  Frame  and  Driving  Mechanism.  The  barrel  shall  be 
mounted  on  a  cast-iron  frame  of  sufficient  strength  and  rigidity 
to  support  it  without  undue  vibration.  It  shall  rest  on  a  rigid 
foundation  with  or  without  the  interposition  of  wooden  plates, 
and  shall  be  fastened  thereto  by  bolts  at  not  less  than  four 
points.  It  shall  be  driven  by  gearing  whose  ratio  of  driver  to 
driven  is  not  less  than  one  to  four." 

"The  Abrasive  Charge.  The  abrasive  charge  shall  consist  of 
cast-iron  spheres  of  two  sizes.  When  new,  the  larger  spheres 
shall  be  3.75  inches  in  diameter  and  shall  weigh  approximately 
7.5  pounds  (3.40  kg.)  each.  Ten  spheres  of  this  size  shall  be 
used.  These  shall  be  weighed  separately  after  each  ten  tests, 
and  if  the  weight  of  any  large  sphere  falls  to  7  pounds  (3.175  kg.), 
it  shall  be  discarded  and  a  new  one  substituted;  provided, 
however,  that  all  of  the  large  spheres  shall  not  be  discarded 
and  substituted  by  new  ones  at  any  single  time,  and  that  so 
far  as  possible  the  large  spheres  shall  compose  a  graduated 
series  in  various  stages  of  wear.  When  new,  the  smaller  spheres 
shall  be  1.875  inches  in  diameter  and  shall  weigh  approximately 
0.95  pound  (0.43  kg.)  each.  In  general,  the  number  of  small 
spheres  in  a  charge  shall  not  fall  below  245  nor  exceed  260. 
The  collective  weight  of  the  large  and  small  spheres  shall  be  as 
nearly  300  pounds  as  possible.  No  small  sphere  shall  be  re- 
tained in  use  after  it  has  been  worn  down  so  that  it  will  pass 
a  circular  hole  1.75  inches  in  diameter,  drilled  in  an  iron  plate 
%  inch  in  thickness,  or  weigh  less  than  0.75  pound  (0.34  kg.). 
Further,  the  small  spheres  shall  be  tested  by  passing  them 
over  the  above  plate  or  by  weighing  after  every  ten  tests,  and 
any  which  pass  through  or  fall  below  the  specified  weight  shall 
be  replaced  by  new  spheres;  provided,  further,  that  all  of  the 
small  spheres  shall  not  be  rejected  and  replaced  by  new  ones 


APPENDIX   III  497 

at  any  one  time,  and  that  so  far  as  possible  the  small  spheres 
shall  compose  a  graduated  series  in  various  stage's  of  wear. 
At  any  time  that  any  sphere  is  found  to  be  broken  or  defective 
it  shall  at  once  be  replaced." 

"OPERATION  OF  THE  TEST.  The  Brick  Charge.  The 
number  of  bricks  per  test  shall  be  ten  for  all  bricks  of  so- 
called  'block-size/  whose  dimensions  fall  between  8  and  9 
inches  in  length,  3  and  3^  inches  in  breadth,  and  3^  and 
4j^  inches  in  thickness.  No  brick  should  be  selected  as 
part  of  a  regular  test  that  would  be  rejected  by  any  other 
requirements  of  the  specifications  under  which  the  purchase  is 
made."  (Note  by  Author.  Each  brick  should  be  marked  by 
small  holes  drilled  in  one  of  the  faces  of  the  brick.  The  initial 
weight  of  each  brick  composing  the  charge  should  be  determined.) 

"Speed  and  Duration  of  Revolution.  The  rattler  shall  be 
rotated  at  a  uniform  rate  of  not  less  than  29.5  nor  more  than 
30.5  revolutions  per  minute,  and  1,800  revolutions  shall  con- 
stitute the  test.  A  counting  machine  shall  be  attached  to  the 
rattler  for  counting  the  revolutions.  A  margin  of  not  to  exceed 
ten  revolutions  will  be  allowed  for  stopping.  Only  one  start 
and  stop  per  test  is  generally  acceptable.  If,  from  accidental 
causes,  the  rattler  is  stopped  and  started  more  than  once  during 
a  test,  and  the  loss  exceeds  the  maximum  permissible  under  the 
specifications,  the  test  shall  be  disqualified  and  another  made." 

*  The  Scales.  The  scales  must  have  a  capacity  of  not  less 
than  300  pounds,  and  must  be  sensitive  to  0.5  ounce,  and  must 
be  tested  by  a  standard  test  weight  at  intervals  of  not  less  than 
every  ten  tests." 

"  The  Results.  The  loss  shall  be  calculated  in  percentage 
of  the  initial  weight  of  the  brick  composing  the  charge.  In 
weighing  the  rattled  brick,  any  piece  weighing  less  than  i  pound 
shall  be  rejected."  (Note  by  Author.  The  loss  should  also  be 
calculated  in  percentage  of  the  initial  weight  of  each  brick 
composing  the  charge.) 


INDEX* 


Abrasion  test 

Gravel,  489 

Rock,  162,  489 

Slag,  489 
Absorption 

Test  for  brick,  349 

Test  for  rock,  164,  488 

Test  for  wood  block,  335 
Administration 

Alabama,  31 

Boston,  37 

California,  31 

Connecticut,  31 

Early  Grecian  highways,  2 

Early  Roman  highways,  2 

France,  25 

Georgia,  32 

Germany,  28 

Great  Britain,  28 

Illinois,  32 

Maryland,  32 

Massachusetts,  33 

Methods  of  financing,  17 

New  Jersey,  34 

New  York,  34 

Ohio,  35 

Pennsylvania,  35 

Providence,  38 

Rhode  Island,  36 

St.  Louis,  38 

Switzerland,  29 

United  States,  30 
^Esthetics,  highways,  48 
Alcatraz,  202 
American  highways,  early 

Cumberland  Road,  15 

Early  highways,  Boston,  13 

Early  legislation,  New  York,  13 

Highways  of  Peru,  13 

Lancaster  Turnpike,  14 


American  highways,  early 

Paving,  15 

York  Road,  14 

American  Society  of  Civil  Engineers, 
Special  Committee  on  Ma- 
terials for  Road  Construction 

Bitumen    and    bituminous    ma- 
terial, 195 

Nomenclature,  192 

Report  forms,  402,  403 

Tests   of   bituminous   materials, 
466-485 

Traffic  classification,  60 

Type  and  blanket  specifications 
for  bituminous  materials,  225 
American  Society  of  Municipal   Im- 
provements 

Pressure  distributors,  254 

Sheet  asphalt  repairs,  310 
American    Society    for   Testing    Ma- 
terials,  Committee  on  Stand- 
ard Tests  for  Road  Materials 

Abrasion  test  for  rock,  489 

Absorption  of  water  test,  488 

Distillation  test,  478 

Solubility   in   carbon   disulphide 
test,  471 

Specific  gravity  of  rock,  486 

Toughness  test  for  rock,  490 

Voids  in  mineral  aggregates,  494 
Ancient  highways 

America,  13 

Assyria,  I 

Britain,  10 

Carthage,  2 

France,  7 

Greece,  2 

Rome,  2 

Spain,  8 


*  Prepared  by  Mr.  W.  C.  Fry,  Jr.,  C.E.,  A.M.,  Instructor  in  Highway  Engineering,  Poly- 
technic Institute  of  Brooklyn  and  Assistant  Engineer  with  A.  H.  Blanchard. 

499 


500 


INDEX 


Asphalt 

Alcatraz,  202 

Bermudez,  199,  200 

Cuban,  201 

Gilsonite,  202 

Lists  of  tests,  211,  212 

Maracaibo,  201 

Mexican,  198 

Oil  asphalts,  204 

Production  of,  198-204 

Rock,  196 

Sources  of,  196 

Specification,  225 

Trinidad,  199 

See  also  Asphalt  cement 
Asphaltenes,  452 
Asphalt  block  pavement 

Composition  of  blocks,  274,  287 

Cost  of,  294 

Manufacture  of,  287 

Maximum  grade  of,  85 

Size  of  blocks,  274,  287 

Tests  of  blocks,  287 

See  also  Comparison  of  roads 

and  pavements 
Asphalt  cement 

Value  of  naphtha  solubility  test, 
219 

See  also  Sheet  asphalt  pave- 
ment 
Asphaltic  petroleums 

Construction  of  bituminous  sur- 
face with,  237 

Fixed  carbon  in,  221 

Methods  of  testing,  466-485 

Occurrence  of,  204 

Specific  gravity  of,  215 

Use  of,  for  dust  prevention,  235, 
236 

Value  of  evaporation   test,   220 

Value    of    flash    point    test,    215 

Value  of  naphtha  solubility  test, 
219 

See  also  Bituminous  materials 

Dust  prevention 

Association    for    Standardizing    Pav- 
ing Specifications 

Asphalt  block  specification,  274 


Belgian  block  pavement,  363 

See  also  Stone  block  pavement 
Benefits  of  improved  highways,  17 
Bermudez  asphalt 

Analysis  of,  200 

Description  of  deposit,  199 
Bins,  stone,  173 
Bitulithic  pavement 

Construction  of,  274 

Cost  data,  293 

Mineral  aggregate,  275 

See  also  Bituminous  concrete 

pavement 
Bitumen 

Bitumen  content,  278 

Extraction  of,  279 

Gilsonite,  202 

Test  for,  218,  469 
Bituminous  concrete  pavement 

Abbott  patent,  283,  284 

Advantages  of,  294 

Asphalt  block,  274,  287,  294 

Bitulithic,  274,  293 

Bitumen  content,  278 

Bituminous  materials,  277 

Causes  of  failure,  295 

Classification  of,  268 

Cost,  277,  293 

Covering,  284 

Crown  of,  91,  92 

Development  of,  267 

Disadvantages  of,  295 

Drying  aggregate,  275,  290 

Excelsior  pavement,  272 

Extraction  of  bitumen,  279 

Foundations,  126,  280 

Heating     bituminous     material, 
275,  281,  282 

Limiting  grades,  84-86 

Mathews  patent,  269 

Mechanical  appliances,  287-292 

Mineral  aggregates,  268 

Mixing,  275,  282 

Mixing  machines,  287,  289-292 

Proportions,  273-275,  282 

Rolling,  270,  282 

Seal  coat,  283,  286,  287 


INDEX 


501 


Bituminous  concrete  pavement 

Size  of  aggregate,  269-271,  273, 

274 

Specifications,  Rhode  Island,  270 
Spreading,  282 
Subgrade,  280 
Tarmac,  276 
Thickness,  269,  270 
Topeka,  273,  293 
See  also  Comparison  of  roads 

and  pavements 

Bituminous  gravel  pavement,  260 
See  also  Bituminous  macadam 

pavement 
Comparison  of  roads  and 

pavements 

Bituminous  macadam  oavement 
Advantages  of,  262 
Amount  of  bituminous  material, 

258-260      ... 
Applying    bituminous    material, 

257-260 

Bituminous  materials  used,   253 
Causes  of  failure,  264 
Cost  data,  261 
Covering,  257-260 
Crown  of,  91,  92,  257 
Development  of,  253 
Disadvantages  of,  263 
Gladwell  system,  259 
Limiting  grades,  84-86 
Maintenance  of,  261 
Modern  pavement,  259 
Pitchmac,  259,  260 
Preparation  of  subgrade,  253 
Repairing  pot  holes,  262 
Rolling,  257-260 
Seal  coat,  257,  259 
Size    of    stone,    254,    257-260 
Thickness  of  courses,  254,  257- 

260 
See  also  Comparison  of  roads 

and  pavements 
Bituminous  materials 
Alcatraz,  202 
Asphalts,  193 
Asphalt  cement,  194 
Bermudez  asphalt,  199 


Bituminous  materials 

California  asphalt,  198,  202 

Coke  oven  tar,  209 

Creosote,  210 

Crude  coal  tar,  207 

Cuban  asphalt,  201 

Cut-back  products,  193 

Distillation  test,  218,  478 

Ductility  test,  214,  481 

Evaporation  test,  220,  478 

Extraction  of  bitumen,  279 

Fixed  carbon  test,  214,  221,  483 

Flash  point  test,  213,  215,  468 

Float  test,  213,  217,  474 

Flux,  193 

Gilsonite,  202 

Joint  fillers,  339,  358 

Maracaibo  asphalt,  201 

Melting  point  test,  213,  216,  476 

Mexican  asphalt,  198 

Oil  asphalts,  204 

Paraffin  test,  214,  222,  483 

Penetration  test,  214,  475 

Refined  coal  tar,  207 

Rock  asphalts,  194,  196 

Solubility,     carbon     disulphicle, 
218,  469 

Solubility,  carbon    tetrachloride, 
472 

Solubility,     88     degree     Baume 
naphtha,  219,  482 

Specific  gravity,  215,  466 

Tars,  194,  206 

Trinidad  asphalt,  199 

Types     used,     bituminous    con- 
crete, 277 

Types  used,   bituminous   maca- 
dam, 253 

Types     used,     bituminous     sur- 
faces, 237 

Viscosity  test,  213,  472 

Water  gas  tar,  209 
Bituminous  surfaces 

Advantages  of,  247 

Amount  of  bituminous  material, 
237,  239 

Applying    bituminous    material^ 
239 


502 


INDEX 


Bituminous  surfaces 

Cost  of,  240 

Crown  of,  91,  92 

Danger  to  fish  life,  249 

Development  of,  227 

Disadvantages  of,  249 

Failures,  250 

Gravity  vs.  pressure  distri- 
bution, 239 

Injury  to  vegetation,  249 

Maintenance  of,  240 

Materials  used,  251 

Mechanical  appliances,  see  Dis- 
tributors 

On  brick  pavement,  360 

On    cement-concrete    pavement, 

324 

Preparation  of  road  surface,  237 

Slipperiness,  249 

Top  dressing,  240 

Use  of,  237 

See   also    Comparison    of    roads 

and  pavements 
Boiler,  173 
Bond  issues,  23 
Brick 

Absorption  test,  349 

Brick  clay,  345 

Brick  shales,  345 

Cross  breaking  test,  349 

Manufacture,  345 

Rattler  test,  349,  495 

Repressed  brick,  347 

Size  and  character  of,  348 

Wire-cut-lug,  345,  347 

See  also  Brick  pavement 
Brick  pavement 

Asphalt  filler,  354 

Bituminous  filler,  358 

Bituminous  surface  on,  360 

Characteristics,  361 

Coal  tar  filler,  354 

Cost  data,  358 

Cross  section  of,  351 

Crown  of,  91,  92,  353 

Development  of,  344 

Expansion  joints,  354 

Foundation,  350 


Brick  pavement 

Grout  filler,  354,  359 

Joint  filler  can,  358,  359 

Laying  the  brick,  352 

Maintenance  of,  360 

Maximum  grade,  84-86 

Rolling,  353 

Sand  cushion,  352 

Sand  joint  filler,  354 

See  also  Brick 

Comparison     of     roads 
and  pavements 
Bridges 

Bridge  floors,  434 

Concrete,  436 

Concrete  arches,  437 

Concrete  girders,  436 

Design,  433 

Formula  for  run-off,  422 

Guard  rails,  437 

I-Beam,  435 

Location,  433 

Measurement  of  flow,  423 

Myer's  formula,  422 

Observation  high  water,  422 

Pin  connected,  436 

Plate  girder,  435 

Pony  truss,  435 

Reinforced  concrete,  436 

Riveted  truss,  436 

Selection  of  type,  433 

Size  drainage  area,  421 

Talbot  formula,  422 

Timber,  436 

Types  of,  432 

Wearing  surface,  434 
British  highways,  ancient,  10 
Broken  stone 

Mechanical  analysis,  493 

Size  of,  178,  179 

Tests  of,  see  Rocks 

Voids,  174,  494 

Weights,  174 

See  also  Broken  stone  roads 
Broken  stone  roads 

Applying  screenings,  183 

Broken  stone  foundation,  122 

Causes  of  wear,  186 


INDEX 


503 


Broken  stone  roads 

Characteristics,  191 

Cost  of,  1 84 

Cross  section  of,  180 

Crown  of,  91,  92,  180 

Crushing  the  rock,  168 

Depth  of  stone,  181,  182 

Effect  of  motor  traffic  on,  51,  52 

Foundation,  179 

Hauling  stone,  181 

History,  175 

McAdam's  principles,  176 

Preparation  of  subgrade,  179 

Quarrying  the  rock,  168 

Ravelling,  187 

Regulating  the  thickness,  182 

Repairing  pot  holes,  188 

Resurfacing,  190 

Rock  classification,  154 

Rock  testing,  161,  486-492 

Rollers,  183 

Rolling,  182 

Scarifiers,  190 

Shoulders,  189 

Size  of  stone,  178 

Spreading  stone,  181 

Telford  foundation,  121,  179 

Tresaguet's  principles,  175 

V-drain  foundation,  179 

Voids  in  stone,  174,  494 

Weights  of  stone,  174 

See  also  Comparison  of  roads 

and  pavements 
Brooms 

Brass  brooms,  238 

Push  brooms,  377 

Sweeping  machines,  378 
Burnt  clay  roads,  136 
Calcium  chloride,  232 
California  asphalt,  198,  202 
Carpet 

See  Bituminous  surfaces 
Car  tracks 

Clearances,  442,  443 

Construction,  443,  444 

Drainage,  446 

Location,  442 

Rails,  443 


Car  tracks 

Rail  joints,  444 

Surfacing  adjacent  to  rails,  446- 
448 

Track  foundation,  445 

Width  occupied  by,  442,  443 
Cart 

See  Wagon 
Catch  basin,  427 
Cement 

See  Concrete 
Cement-concrete  pavement 

Bituminous  surface  on,  324,  325 

Blome  pavement,  319 

Characteristics,  327 

Concrete  cubes,  317 

Cost  data,  325 

Crown  of,  91,  92,  317 

Development  of,  315 

Expansion  joints,  320-322 

Foundation,  316 

Grouting  method,  323 

Hassam  pavement,  322,  323 

Ingredients,  315 

Maintenance,  326 

Mileage,  315 

Mineral  aggregates,  315 

Oil  cement-concrete,  320 

One  course  method,  319 

Proportioning  concrete,  315 

Reinforced  pavement,  320 

Subgrade  of,  316 

Two  course  method,  319 

See    also    Comparison    of    roads 

and  pavements 
Cementation  test,  162,  492 
City  planning 

See  Design 
Clay 

Adaptability,  129 

Brick,  345 

See  also  Soils 
Clinker  pavement,  373 
Coal  tar 

Analysis  of,  206 

Blowing,  208 

Danger  to  fish  life,  249 

Distillation,  208,  218,  478 


504 


INDEX 


Coal  tar 

Free  carbon  in,  206 
Injury  to  vegetation,  249 
Methods  of  testing,  466-485 
Pitches,  208 
Production  of,  206 
Refined  tar,  207 
Removing  water,  207 
Retorts,  207 

Source  of  crude  tar,  206,  207 
Specific  gravity,  215,  466 
Tar  stills,  207,  208 
Cobblestone  pavement,  372 
Coke  oven  tar,  194 

Manufacture,  209 

Comparison  of  roads  and  pavements 
Annual  cost,  396 
Cost  records,  400,  401 
Effect  of  grade,  394 
Hay  wood  report,  393 
Ideal,  390 

Life  of  pavements,  390,  391 
Maximum  grades,  393-396 
Methods  of  comparison,  398 
Noiselessness,  392 
Report  forms,  402,  403 
Resistance  to  traffic,  393 
Sanitary  qualities,  392 
Scientific  comparison,  389 
Slipperiness,  392 
Suitability  of  types,  391,  399 
Concrete 

Grouting  method,  126,  323 
In  situ  method,  125 
Mixing,  123-126,  317 
Proportions  of,  123,  315 
See  also  Cement-concrete  pave- 
ment 

Foundation 
Sidewalk 
Conduits 

See  Pipe  systems 
Convict  labor,  18 
Cost 

See  Material,  road  or  pavement 
Crown,  91,  92 

See  also  Road  or  pavement 


Crushers 

Bins,  173 
Boiler,  173 
Elevator,  173 
Engine,  173 
Gyratory,  172 
Jaw,  172 
Screen,  173 
Crushing 

Crushers,  171 
Crushing  plant,  171 
Cuban  asphalt,  201 
Culvert 

Arch,  432 
Cast  iron  pipe,  426 
Concrete  pipe,  427 
Corrugated  metal  pipe,  426 
Design,  424 
Foundation,  425 
Formula  for  run-off,  422 
Headwalls,  425 
High  water  mark,  422 
Location  of,  424 
Measurement  of  flow,  423 
Myer's  formula,  422 
Reinforced  concrete,  430,  431 
Selection  of  type,  423 
Size  of  drainage  area,  42 1 
Stone  box,  430 
Talbot  formula,  422 
Timber  box,  432 
Vitrified  pipe,  426 
Cumberland  Road,  15 
Curbs 

Concrete,  417 
Cost,  417,  418,  420 
Curb  elevations,  87 
Dimensions,  417 
Laying,  417 
Radii  corners,  417,  418 
Staking  out,  74 
Stone,  417 
Curves 

Elimination  of,  88 
Radii  of,  88,  89 
Stationing,  65 
Vertical,  87 
Width  of  road  on,  88 


INDEX 


505 


Cut-back  products,  193 
Danger  signs,  440 
Design 

City  highway  systems,  76 

Crowns,  91,  92 

Curb  elevations,  87 

Curves,  88 

Determination  of  grade,  84 

Determination  of  width,  80 

Drainage,  45,  111-117 

Effect,  horse-drawn  traffic,  50 
"       motor  trucks,  52 
motor  vehicles,  51 
traction  engines,  54 

Estimates,  93 

Foundation,  44,  117 

Influence  of  aesthetics,  48 
of  climate,  47 
of  locality,  48 
of  maintenance  meth- 
ods, 47,  48 
of  traffic,  49-63 

Loads  and  tire  widths,  55 

Location,  79 

Park  highway  systems,  78 

Scope  of  design,  78 

State  highway  systems,  75 

Street  intersections,  87 

Street  systems,  75 

Use  of  local  materials,  47 

Vertical  curves,  87 

Width,  80 

Deval  machine,  161,  489 
Direction  signs,  440 
Distance  signs,  440 
Distillation  test,  218,  478 
Distributors 

Amount  of  pressure,  254 

For  spraying  light  oils,  234 

Gravity,  241 

Hand-drawn,  242,  243,  245 

Pouring  cans,  241,  242 

Pressure  distributors,  244 

Specifications,  American  Society 
of    Municipal    Improvements, 

254 

Ditch,  115,  130 
Dorry  machine,  164,  166,  491 


Drag  scraper 

Description,  101 

Method  of  operation,  101 
Drainage 

Blind  drains,  115 

Catch-basins,  427 

Concrete  pipe  subdrains,  427 

Conditions  encountered,  112 

Drop  inlets,  427 

Earth  roads,  130,  131 

Frost  action,  113 

Gutters,  115 

Inlet  castings,  429 

Laying  the  pipe,  114 

Object  of,  in 

Preliminary  examination,  45 

Side  ditches,  115,  130 

Size  of  pipe,  113 

V-drain,  121 
Drilling,  168 
Drop  inlet,  427 
Ductility  test,  214,  481 
Durax  pavement 

Foundation,  366,  370 

Joint  fillers,  370 

Manufacture  of  blocks,  364 

Size  of  blocks,  364 
Dust  palliatives 

Calcium  chloride,  232 

Classification  of,  231 

Definition  of,  227 

Emulsion,  234 

Light  oils  and  tars,  235 

Use  of,  230 

Water,  231 

See  also  Dust  prevention 
Dust  prevention 

Calcium  chloride,  232 

Effects  of  dust,  228 

Emulsions,  234 

Formation  of  dust,  228 

Light  oils  and  tars,  235 

Pathogenic  effects  of  dust,  229 

Preparation  of  road  surface,  237 

Use  of  palliatives,  230 

Water,  231 
Earthwork 

Balancing  cuts  and  fills,  85 


506 


INDEX 


Earthwork 

Earth  shrinkage,  97 
Estimating  volume,  93 
Grading  classification,  96 
Moving  with  drag  scrapers,  101 
elevating      grader, 
104 

road  scrapers,  102 
wagons,  98 
wheel  scrapers,  102 
Earth  road 

Construction  with  elevating  gra- 
der, 131 
Cost  of,  134 
Cross-section  of,  131 
Crown  of,  91,  130,  131 
Directions  for  building,  129 
Drainage  of,  129 
Earth  shrinkage,  97 
Grading  classification,  96 
Maintenance,  137 
Mileage  in  U.  S.,  128 
Road  drag  law  (Illinois),  139 
Road  dragging,  138 
Slopes  of  banks,  95 
Wearing  course  of,  132 
See  also  Comparison  of  roads  and 

pavements 
Economics 

Annual  cost,  397 

Bond  issues,  23 

Convict  labor,  18 

Direct  appropriation,  22 

Direct  taxation,  19 

Labor  tax  system,  18 

Private  subscription,  24 

See  also  Comparison  of  roads  and 

pavements 
Elevating  grader 

Description  of,  104 
Method  of  operation,  104 
See  also  Earth  road 
Elevator,  crushing  plant,  173 
Embankment 

Construction  of,  94 
Shrinkage  of,  97 
See  also  Earthwork 


Emulsion,  234 

See  also  Dust  prevention 
Engine,  crushing  plant,  173 
Estimating 

Balancing  cuts  and  fills,  85 
Cross-sections,  72 
Earthwork,  93 
See  also  Design 
Evaporation  test,  220,  478 
Excelsior  pavement,  272 
Explosive,  170 
Fieldstone,  160 

Fixed  carbon  test,  214,  221,  483 
Flash  point  test,  213,  215,  468 
Float  test,  213,  217,  474 
Flushing 

Flushing  machines,  379 
Hose  flushing,  379 
Squeegees,  379 
See  also  Street  cleaning 
Flux,  193 
Footway 

See  Sidewalk 
Foundation 

Bituminous  concrete,  126 
Broken  stone,  122 
Classification  of,  1 1 8 
Concrete,  122 
Examination,  117 
Importance  of,  117 
Methods  of  improving,  120 
Over  marshes,  126 
Proposed  by  McAdam,  176 
Tresaguet,  175 
Rolling,  121 
Safe  loads  on,  120 
Soil  classification,  118 
Telford,  121 

Use  of  old  pavement,  126 
V-drain,  121 
French  highways,  ancient 

Condition  of  early  highways,  7 
Corvee  system,  9 
Tresaguet 's  method,  10 
Frost,  action  of,  113 

See  also  Drainage 
Gas  pipes 

See  Pipe  systems 


INDEX 


507 


Joint  filler 

See  Brick  pavement 

Stone  block  pavement 
Wood  block  pavement 
Karri  wood,  330 
Kleinpflaster  pavement 

Foundation,  367 

Manufacture  of  blocks,  364 

Size  of  blocks,  366 
Legislation,  highway   . 

Alabama,  31 

California,  31 

Connecticut,  31 

France,  25 

Great  Britain,  28 

Illinois,  32 

Loads  and  tire  widths,  55,  56 

Maryland,  32 

Massachusetts,  33 

New  Jersey,  34 

New  York,  34 

Ohio,  35 

Pennsylvania,  35 

Rhode  Island,  36 
Levelling 

Bench  marks,  68 

Information  desired,  68 

Plotting  profile,  72 

Running. levels,  68 

See  also  Surveys 
List  of  tests,  211 
Loads 

Commerical  motor  trucks,  56 

Heavy  loads,  New  York  City,  56 

Loads  on  foundation,  120 

Motor  car  order  of  England  lim- 
iting, 56 

See  also  Design 
Loam,  119 
Location, 

Esthetics  and  location,  48 

Bridges,  433 

Culverts,  424 

Pipes,  see  Pipe  systems 
Macadam  road 

See  Broken  stone  road 
Maintenance 

See  Road  or  pavement 


Mapping 

Cross-sections,  72 
Drawing  the  grade,  85 
Plan  of  road  surveys,  70 
Profile  of  road  surveys,  72 
Street  surveys,  74 
Topography,  74 
Maracaibo,  201 
Marl,  119 
Marsh  road,  126 

See  also  Earth  road 
McAdam 

Principles  of  construction,  1 1, 176 
Mechanical  analyses 

Broken    stone,    broken    slag    or 

gravel,  144,  493 

Mixtures   of    sand    with    broken 
stone,  broken  slag  or  gravel,  494 
Sand,  493 
Medina  sandstone 

See  Stone  block  pavement 
Melting  point  tests,  213,  216,  476 
Mexican  asphalt,  198 
Mineral  aggregates 

Bituminous  concrete    pavement, 

268 

Mechanical  analyses,  493,  494 
Voids,  494 

Mixing  machinery,  124,  125,  289 
Mixing  method 

Hand    mixing    cement-concrete, 

124 
Machine  mixing  cement-concrete, 

124 
See  also  Bituminous  concrete 

pavement 

Sheet    asphalt    pave- 
ment 
Motor  trucks 

Effect  on  highways,  51,  52 
Loads  carried  by,  56 
See  also  Design 
Muck,  119 

National     Paving     Brick     Manufac- 
turers' Association 
Fillers  for  brick  pavement,  354 
Foundation  for  brick  pavement, 
351 


508 


INDEX 


Gilsonite,  202 
Glossary,  451-465 
Grade 

Curb,  74 

Drawing,  85 

Maximum,  85 

Minimum,  85 

Recording  grade  stake  notes,  69, 
70 

Relation  grade  to  location,  45 

Setting  slope  stakes,  70 

Staking,  69 

Vertical  curves,  87 

See  also  Design 
Grader 

See  Elevating  grader 
Grading 

Classification  of  materials,  96 

Surveying  for,  69 

See  also  Earthwork 

Earth  roads 
Granite 

Composition  of,  157 
Granite  block  pavement 

See  Stone  block  pavement 
Gravel 

Abrasion  test,  489 

Bank  gravel,  141 

Binder  in,  143 

Definition  of,  141 

Formation,  142 

Mechanical    analysis,    144,    145, 

493,  494 

Quality  of  stone,  145 
Requisites,  142 
Results  of  analysis,  145 
Rolling,  151 
Sampling,  144 
Screening,  150 
Spreading,  151 
Voids  in,  145,  494 
Gravel  road 

Binder,  143 
Cost  of,  152,  153 
Cross-section  of,  150 
Crown,  91,  92,  146 
Depth  of,  146,  148 
Gravel,  141-143 


Gravel  road 

Maintenance  of,  152 

Mileage  of,  141 

Patching,  153 

Preparation  of  subgrade,  145 

Resurfacing,  153 

Rolling,  151 

Spreading  the  gravel,  151 

Surface  method,  146 

Testing  the  gravel,  144,  489 

Thickness,  148,  149 

Trench  method,  147 

See  also  Comparison  of  roads  and 

pavements 

Grecian  highways,  ancient,  2 
Guard  rail 

Concrete,  439 

Location,  437 

Parapet  wall,  439 

Pipe,  438 

Wood,  437 
Gutter 

Cost,  419,  420 

Depth  of,  419 

Materials  used,  418 

Methods  of  construction,  418- 

Necessity  for,  418 

Widths,  419 
Hand  mixing,  124 
Hardness  test,  491 
Heater,  surface,  311,  312 
Highway,  44. 

Highway  department  signs,  440 
History,  pavement 

Bituminous  concrete,  246 
macadam,  253 
surface,  227 

Brick,  344 

Broken  stone,  12,  175 

Cement-concrete,  315 

Dust  palliatives,  227 

Sheet  asphalt,  298 

Stone  block,  363 

Wood  block,  328 
Horse,  pull  exerted  by,  84,  395. 
Horse-drawn  traffic 

Effect  on  highways,  50 
Jarrah  wood,  330 


INDEX 


509 


Noiselessness,  392 
Oiled  road 

See  Dust  prevention 
Organization 

State  and   county  departments, 

39 

Urban  district  departments,  41 
Paraffin  test,  214,  222,  483 
Park  highways,  78 

See  also  Design 
Peat,  119 
Penetration  method 

See  Bituminous  gravel  pavement 
Bituminous  macadam  pave- 
ment 

Penetration  test,  214,  475 
Petroleum,  204 
Petrolithic  road,  137 
Pipe  drain 

Cost  of,  115 

Grade  of,  115 

Laying,  114 

Size  of,  113,  114 

Tile,  114 
Pipe  systems 

Kinds  of,  448 

Location,  449 

Pipe  subways,  449 

Repaving  trenches,  450 

See  also  Design 
Pitchmac,  259,  260 
Plow 

Grading  plow,  101 

See  also  Earthwork 
Pouring  can,  241 
Preliminary  investigation 

^Esthetics,  48 

Climatic  conditions,  47 

Drainage,  45 

Foundation,  45 

Local  environment,  48 

Local  materials,  47 

Location,  45 

Maintenance,  47 

Traffic,  49-53 

Width,  46 
Preserving  timber 

See  Wood  block 


Quarrying 

Blasting,  170 

Churn  drills,  168* 

Cost  of  drilling,  168 

Hammer  drills,  168 

Stripping  quarry,  168 
Railway 

See  Car  tracks 
Rattler  test,  349,  495 
Ravelling 

See  Broken  stone  road 
Reinforced  concrete 

See  Bridge 

Cement-concrete  pavement 
Culvert 
Road  administration 

See  Administration 
Economics 
Legislation 
Road  drag 

Drags  vs.  scrapers,  138 

Lap  plank  drag,  99 

Method  of  operation,  100 

Plank  drag,  99 

Split  log  drag,  98 

Steel  drags,  100 
Road  machinery 

See  Machine  or  tool 
Road  scraper 

Description,  103 

Method  of  operation,  103 
Road  taxes,  20 
Rocks 

Abrasion  test,  162,  489 

Absorption  test,  164,  488 

Apparent    specific    gravity   test, 
486 

Aqueous,  154,  451 

Ball  mill,  492 

Basalt,  452 

Breccia,  454 

Cementation  test,  492 

Cementing  value,  162 

Definitions,  154 

Deval  machine,  161,  489 

Diorite,  156 

Dorry  machine,  164,  166,  491 

Fieldstone,  160 


510  INDEX 

Rocks  Sand 

French  coefficient,  162  Apparent    specific   gravity   test. 

Gneiss,  159  487 

Granite,  157,  160  Definition  of,  118,  141 

Hardness  test,  164,  491  Mechanical  analysis  of,  144,  145, 

Igneous,  154  493,  494 

Impact  machines,  162,  163  Sand  cushion,  336,  352 

Limestone,  159,  160  Sand  filler,  338,  354 

Mechanical  analysis,  493  Wearing  surface,  sheet  asphalt, 

Metamorphic,  154  302 

Microstructure,  157  See  also  Soils 

Mineral  constituents,  155,  158  Sheet  asphalt  pavement 

Properties  rocks  should  possess,       Sand-clay  road 

1 60  Clayey  subsoil,  136 

Results  of  tests,  164,  167  Construction,  129 

Rock  classification,  154  Cost  of,  134 

Rock  testing,  161,  486-492  Cross-section  of,  131 

Sandstone,  159,  160  Drainage  of,  129 

Schist,  159  Maintenance,  137 

Slate,  1 60  Mileage  constructed,  128 

Specific  gravity  test,  164,  486  Road  dragging,  138 

Syenite,  159  Sandy  subsoil,  135 

Tests,  161,  486-492  Wearing  course,  134 

Toughness,  164  See  also  Comparison  of  roads  and 

Toughness  test,  490  pavements 

Trap,  156,  1 60  Earth  roads 

See  also  Crushing  Scarifier,  109 

Quarrying  Schutte  method,  voids,  175 

Rock  asphalt  pavement  Screen 

American  practice,  305  Rotary  screen,  173 

Borough  of  Manhattan  specifica-  Sizes,   mechanical  analysis,    144, 

tions,  305  178,493 

Broken  rock  asphalt,  305  Sea  water,  232 

Crown  of,  91,  92  See  also  Dust  prevention 

European  practice,  303  Sewer 

Powdered  rock,  305  See  Pipe  systems 

Rock  asphalts  of  Europe,  196  Shale,  119 
Use  of  rock  asphalt,  298,  303,  305       Sheet  asphalt  pavement 

See  also  Comparison  of  roads  and  Action  of  gas  leaks,  309 

pavements  "  water,  308 

Roller  Asphalt  cement,  218,  299 

Horse  roller,  106  Asphalt  plants,  303 

Tandem  roller,  109  Binder  stone,  300 

Three  wheel,  109  Causes  of  failure,  306 

Roman  highways,  ancient,  2-7  Construction,  302 

Sand  Cost  of,  306 

Adaptability  for  road  construe-  Cross-section  of,  298 

tion,  129  Crown  of,  91,  92 


INDEX 


511 


Sheet  asphalt  pavement 

Defects  in  construction,  309 

Development  of,  298 

Effect   of  ageing  and   exposure, 
308 

Filler,  301 

Flux,  300 

Foundation,  122,  126,  302,  309 

Heating  asphalt  cement,  303 

Laying  binder,  302 

Maximum  grade  of,  85 

Patching,  312 

Preparation  binder  course,  302 

Preparation  wearing  surface,  302 

Repairing,  310,  312 

Sand,  wearing  surface,  301 

Subgrade,  302 

Surface  heater,  311,  312 

Tandem  roller,  303 

Traffic  deterioration,  307 

See  also  Comparison  of  roads  and 

pavements 
Shell  road, 

Construction  of,  185 
Shoulder 

Construction  of,  189 

Slopes  of  banks,  131 
Sidewalk 

Asphalt  mastic,  407 

Brick  and  tile,  407 

Cement-concrete,  409 

Cinders,  409 

Cost  of,  407,  408,  413 

Cross-section  of,  408,  410 

Essential  qualities,  406 

Foundation,  409,  416 

Gravel,  414 

Slope  of,  406 

Small  stone  setts,  414 

Stone  flagging,  414 

Tar  concrete,  415 

Width  of,  406 
Signs 

Danger  signs,  440 

Direction  and  distance  signs,  440 

Highway  department  signs,  440 

Street  signs,  441 


Slag 

Abrasion  test,  489 

Hardness  test,  491 

Mechanical  analysis,  493,  494 

Toughness  test,  490 
Slag  block  pavements,  373 
Slag  road,  184 
Slipperiness,  392,  393 
Snow  removal 

Flushing,  388 

Machines,  385,  387 

Organizing  labor,  384 

Use  of  plows,  386 

"     "  salt,  388 
Soils 

Bearing  power  of,  120 

Classification  of,  118 

Clay,  119 

Drainage  of,  129 

Loam,  119 

Marl,  119 

Muck,  119 

Peat,  119 

Sand,  118 

Shale,  119 
Solubility  tests 

Carbon  disulphide,  218,  469 

Carbon  tetrachloridc,  472 

Naphtha,  219,  482 
Specifications 

See  Material,  road  or  pavement 
Specific  gravity  test,  215,  466,  486 
Sprinklers 

See  Watering  cart 
Sprinkling 

See  Watering 
Squeegees,  379 
State  highway 

Design  of  system,  75 

Width  of,  82 
Stone  block  pavement 

Belgian  block,  363 

Characteristics,  375 

Cost  data,   United   States,   370, 

37i 

Cross-section  of,  368,  369 
Development  of,  363 
Durax,  364-367 


512 


INDEX 


Stone  block  pavement 

Foundation,  366 

Grout  filler,  370 

Kleinpflaster,  364-367 

Laying  the  blocks,  367 

Maintenance  of,  374 

Manufacture  of  blocks,  364 

Maximum  grade  of,  84,  85 

Sand  cushion,  367 

Sand  joint  filler,  368,  369 

Size  of  blocks,  366 

Stone  used,  364 

Subgrade,  366 

Tar  and  gravel  filler,  369 

Tests  of  blocks,  366 

See  also  Comparison  of  roads  and 

pavements 
Stone  screenings 

Apparent    specific    gravity    test, 

487 

Straw  road,  136 
Street 

Circumferential  plan,  78 

Cross-section  of,  90 

Crowns  of,  91,  92 

Curves,  88 

Design  of  street  intersections,  87 

Maximum  grades,  85 

Minimum  grades,  85 

Rectangular  plan,  77 

Widths,  80 

See  also  Design 

Surveys  for  city  streets 
Street  cleaning 

Bags  and  cans,  376,  378 

Boston,  382 

France,  383 

Germany,  383 

Great  Britain,  382 

Hand  cleaning,  376 

Heavy-traffic  streets,  378 

Hose  flushing,  379 

Light-traffic  streets,  378 

Machine  sweeping,  378 

Motor  truck  sweepers,  378 

New  York  City,  380 

Philadelphia,  381 

Pick-up  sweepers,  379 


Street  cleaning 

Push  brooms,  377 

Rotary  squeegees,  379 

Squeegees,  379 

Sweeping  machines,  378,  379 

Washington,  D.  C,  382 
Street  intersection,  87 
Street  signs,  441 
Subdrain 

See  Drainage 
Subgrade 

See  Road  or  pavement 
Subsurface  structures 

See  Pipe  systems 
Superficial  tarring 

See  Bituminous  surfaces 
Surveys  for  city  streets 

Levels,  73 

Mapping,  74 

Monumenting,  73 

Staking,  74 

Survey  for  grading,  74 

Traverse  method,  73 
Surveys  for  roads 

Final  survey,  70 

General  scope  of  work,  64 

Levels,  68 

Plotting  the  plan,  70 
profile,  72 

Staking  grades,  69 

Stationing  and  referencing,  65 

Taking  topography,  66 

Transit  line,  65 

Use  of  maps,  64 
Sweepers 

Motor  truck,  379 

Pick-up,  379 

Rotary,  379 

See  also  Street  cleaning 
Sweeping 

Motor  truck  sweepers,  379 

Pick-up  sweepers,  379 

Push  brooms,  377 

Preparatory    to    applying    bitu- 
minous surface,  237 

Rotary  sweeper,  379 

Sweeping  snow,  387 

See  also  Street  cleaning 


INDEX 


513 


Tar,  194,  206,  211 
See  also  Coal  tar 

Coke  oven  tar 
Water  gas  tar 
Tarmac  pavement,  276 
Telford 

Construction,  121 

See  also  Broken  stone  road 

Foundation 
Tests 

Bituminous  materials,  466-485 
Non-bituminous  materials,  486- 

497 
Tile 

See  Pipe  drain 
Tires,  55 
Topeka  pavement,  273,  279 

See  also  Bituminous  concrete 

pavement 
Topography 

Cross-section  levels,  68 

Information  desired,  66 

Plotting,  74 

Taking  topography,  66 

See  also  Surveys 
Toughness  test 

Rocks,  164,  490 
Trackway,  371 
Traction,  393-395 
Traffic 

Diversion  of,  62 

Effect,  horse-drawn  vehicles,  50 
motor-car,  51 
motor  truck,  52 
traction  engine,  54 

Elements  of  classification,  49 

Loads  and  tire  widths,  55 

Regulations,  62 

Widths  occupied  by,  80,  82 
Traffic  census 

Classification  of  traffic,  57,  60 

France,  58 

Importance  of,  49 

Methods  used  prior  to  1900,  58 
since  1900,  59,  60 

United  States,  59 
Transit  line 

Running  the  line,  66 


Transit  line  § 

Stationing,  65 

Use  of  as  center  line,  65 

as  reference  line,  65 

See  also  Surveys 
Trap  rock 

Composition  of,  156 

Use  of,  as  road  metal,  160 
Traverse,  73 

See  also  Surveys 
Tresaguet,  10,  175 
Trinidad  asphalt 

Analysis  of  deposit,  200 

Description  of  deposit,  199 
V-drain 

Construction  of,  121 
Viscosity  test 

Engler  viscosimeter,  213,  472 

Float  test,  213,  217,  474 

Penetration,  214,  475 
Voids  test 

American    Society    for    Testing 
Materials  method,  494 

Broken  stone,  174 

New  York  State  method,  174 

Pouring  method,  174 

Schutte  method,  175 

U.    S.    Office   of    Public     Roads 

method,  175 
Volatilization  test 

See  Evaporation  test 
Wagon 

Patent  bottom  dump,  98 

Tip  cart,  98 
Watering 

As  a  dust  layer,  231 

See  also  Dust  prevention 

Street  cleaning 
Watering  cart 

Description  of,  in 
Water  gas  tar 

Manufacture,  crude,  209 

Pitches,  210 
Water  pipe 

See  Pipe  systems 


514 


INDEX 


Waterway 

See  Bridges 
Wheel  scraper 

Description  of,  102 

Method  of  operation,  102 
Width 

See  Design 

Sidewalk 
Wood  block 

Amount  of  preservative,  334,  335 

Causes  of  decay,  330 

Creosote,  331 

Manufacture,  332 

Open  tank  process,  334 

Preservatives  used,  331 

Pressure  process,  334 

Size,  332 

Water  absorption  test,  335 

Wood  preservation,  331 

Woods  used,  329 

See  also  Wood  block  pavement 


Wood  block  pavement 

Bituminous  filler,  339 

Bleeding,  340 

Characteristics  of,  342 

Cost  data,  339,  340 

Cost  of  maintenance,  342 

Development  of,  328 

Expansion  joint,  337 

Foundation,  335 

Grout  filler,  339 

Laying  the  blocks,  337 

Maximum  grade  of,  85 

Mortar  cushion,  336 

Relaying,  341 

Repairs,  341 

Rolling,  337 

Sand  cushion,  336 

Sand  filler,  338 

Subgrade,  335 

See  also  Comparison  of  roads  and 

pavements 
"     "     Wood  block 


fK! 


AM  . 


OCT    4   1932 


oet   f 


21-50.H- 


314623 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


